# Glossary of image and licence terms > Plain definitions of the terms you meet with free images: resolution, DPI, SVG, transparency, IIIF, CC0, CC BY, share-alike, editorial use, model release. ## Images ### Stock photo A photo made once and licensed many times, so designers and writers don't have to shoot everything themselves. It ranges from free public-domain archives to paid libraries that license each image per use. Also: stock image, stock photography. [Search free images](https://image.shep.bot/search) · [Free images for commercial use](https://image.shep.bot/guides/free-images-commercial-use) ### Public-domain art Paintings, prints and drawings whose copyright has expired. Museums such as the Met, the Art Institute of Chicago and the Cleveland Museum of Art release their photographs of these works under CC0, so anyone may reuse them. Also: open access art, museum open access. [Museum open access](https://image.shep.bot/guides/museum-open-access-art) · [Impressionist paintings](https://image.shep.bot/collections/public-domain-impressionist-paintings) ### Botanical illustration A scientifically accurate drawing or print of a plant, often hand-coloured, made for herbals and botany books before photography. Most are now public domain. Also: botanical plate. [Botanical illustrations](https://image.shep.bot/collections/botanical-illustrations) ### Ukiyo-e Japanese woodblock prints of the 17th to 19th centuries (Hokusai, Hiroshige, Utamaro): landscapes, actors and city life in flat colour and bold line. Museum impressions are widely available as CC0. Also: woodblock print, Japanese print. [Japanese woodblock prints](https://image.shep.bot/collections/japanese-woodblock-prints) ### Archive photograph A photograph kept by a library or archive, such as the Library of Congress. Many are public domain, but each comes with a rights statement worth reading, and the people in them can still need clearance for advertising. Also: historical photo, vintage photo. [Vintage city photos](https://image.shep.bot/collections/vintage-city-photographs) ### Icon A small symbol for an action or idea (upload, share, settings). Icons come in sets with a shared style and licence; open-source sets such as Material Symbols, Tabler and Phosphor are searched through Iconify. Also: icon set, pictogram. [Free SVG icons](https://image.shep.bot/collections/free-svg-icons) · [SVG icons and transparent PNGs](https://image.shep.bot/guides/transparent-png-and-svg-icons) ### Illustration A drawn or digitally made picture rather than a photo. Illustrations are often vectors and come with their own licences; museum drawings and prints are listed separately as art. Also: clip art, vector illustration. ### Texture A close-up of a surface (paper, wood, stone, fabric) used as a background or overlay in a design. A seamless texture tiles without visible edges. Also: background texture, pattern. [Paper textures](https://image.shep.bot/collections/paper-textures-backgrounds) ### Composite image An image made from several exposures or wavelengths, common in astronomy: Hubble and Webb pictures map infrared, ultraviolet or X-ray light to visible colours. Say so in the caption when it matters. Also: false colour, representative colour. [Hubble and Webb images](https://image.shep.bot/collections/hubble-space-images) ## Image files ### Resolution An image's width and height in pixels. Image Asset Server groups images by the short side, so a 2160×3840 phone wallpaper counts as 4K, the same as a 3840×2160 desktop one. Also: pixel size, dimensions. ### Megapixels Width times height in millions of pixels. A 6000×4000 photo is 24 MP. More megapixels allow larger prints and tighter crops. Also: MP. ### DPI / PPI Dots or pixels per inch when an image is printed. 300 dpi is the usual target for print: an A4 page (8.3 × 11.7 in) needs about 2480 × 3508 pixels. On screens only the pixel size matters. Also: print resolution, 300 dpi. ### Aspect ratio Width divided by height. 16:9 suits banners and slides, 3:2 is the classic camera frame, 4:5 and 9:16 suit phone screens, 1:1 avatars and social posts. Changing it means cropping. Also: 16:9, 3:2, 4:5, 1:1. ### Orientation Whether an image is landscape (wider than tall), portrait (taller than wide, also called vertical) or square. Within 5% of square counts as square here. ### Vector (SVG) An image described as shapes rather than pixels. It scales to any size without blurring, stays small, and can be recoloured with CSS. Icons, logos, diagrams and maps are often vectors. Also: SVG, scalable vector graphics. [SVG icons](https://image.shep.bot/guides/transparent-png-and-svg-icons) ### Raster image An image made of pixels: photos and scans. JPG compresses photos well; PNG is lossless and supports transparency; WebP and AVIF do both more efficiently. Also: bitmap, JPG, PNG. ### Transparent background Areas of an image with no colour, so whatever is behind shows through. PNG, WebP and SVG support it; JPG does not. Transparent images are shown on a checkerboard on this site. Also: alpha channel, cut-out, PNG transparency. ### TIFF A lossless format used for archival scans and print masters. Files are large (tens of megabytes); museums such as the Cleveland Museum of Art offer TIFFs for print. Also: TIF. ### IIIF A standard image API used by museums and libraries to serve an image at any size or crop from one URL. The Art Institute of Chicago and the Library of Congress use it. Also: International Image Interoperability Framework. [reference](https://iiif.io) ### Resized copy A smaller copy of an image made by the source, such as NASA's 1920 px 'large' JPG or a Wikimedia thumbnail. Quicker to download than the original and usually enough for the web. Also: rendition, derivative. ### Original The file as published by the source, at full size. Download it for print or heavy cropping; for a website a resized copy is lighter. Also: master, full resolution. ### Alt text A short description of an image for people using screen readers and when the image fails to load. Image sets suggest one per pick; write your own when the image carries meaning. Also: alternative text. ## Licences and rights ### Public domain Works no one owns a copyright in, because it expired, was never claimed, or (in the US) the work was made by the federal government. Anyone may use them for anything, though trademarks and the rights of people shown can still apply. Also: PD, Public Domain Mark. [Free images for commercial use](https://image.shep.bot/guides/free-images-commercial-use) · [reference](https://creativecommons.org/publicdomain/mark/1.0/) ### CC0 A Creative Commons tool with which a creator gives up their copyright as far as the law allows, putting the work in the public domain: use it commercially, no credit needed. Museum open-access images use it. Also: CC0 1.0, public domain dedication. [reference](https://creativecommons.org/publicdomain/zero/1.0/) ### CC BY Creative Commons Attribution: use it for anything, including commercial work, as long as you credit the author, name the licence, link it and say if you changed the image. Also: Attribution. [How to credit CC BY images](https://image.shep.bot/guides/credit-cc-by-images) · [reference](https://creativecommons.org/licenses/by/4.0/) ### CC BY-SA Attribution-ShareAlike: like CC BY, but an adapted version of the image must be released under the same licence. Marked Restricted, because most commercial designs edit their images and can't be relicensed that way. Also: share-alike, SA. [reference](https://creativecommons.org/licenses/by-sa/4.0/) ### NC (NonCommercial) A Creative Commons condition that rules out use 'primarily intended for or directed towards commercial advantage or monetary compensation': ads, client work, products you sell. Also: CC BY-NC. [reference](https://creativecommons.org/licenses/by-nc/4.0/) ### ND (NoDerivatives) A Creative Commons condition that forbids sharing adapted versions. Cropping, retouching, putting text on top or compositing an ND image counts as adapting it, so ND images get a 'no' verdict here. Also: CC BY-ND. [reference](https://creativecommons.org/licenses/by-nd/4.0/) ### MIT, Apache 2.0, ISC Software licences used by most open-source icon sets. They allow commercial use and modification; keep the set's copyright and licence notice with copies you distribute, for example in your app's third-party notices. Also: open-source icon licence. [reference](https://opensource.org/license/mit) ### SIL Open Font License A licence used by icon fonts and some icon sets: free to use, embed and modify in any project, but the font or icon files may not be sold on their own. Also: OFL. [reference](https://openfontlicense.org/) ### Royalty free Pay once (or nothing) and use the image without per-use fees. It does not mean copyright free: the licence still sets rules, typically no reselling or re-uploading the image as stock. ### Editorial use Use in articles, books, education and commentary, as opposed to advertising or promotion. Images showing people, logos or insignia without releases are often editorial-only, whatever their copyright licence says. Also: editorial only. [Free images for commercial use](https://image.shep.bot/guides/free-images-commercial-use) ### Model release A signed permission from a recognisable person to use their likeness commercially. Without one, a photo of them is usually fine for editorial use but not for ads or endorsements. ### Property release Permission from the owner of recognisable private property, artwork or a trademark to show it commercially. Logos and branded products in the picture are the most common reason an image is editorial-only. ### Attribution The credit a licence asks for: title, author, source and licence (TASL), with links. Every result that needs one carries a ready-made credit line. Also: credit line, TASL. [How to credit CC BY images](https://image.shep.bot/guides/credit-cc-by-images) ### Rights statement An archive's note on an item's copyright status, such as the Library of Congress's 'No known restrictions on publication' or 'Rights status not evaluated'. It is the archive's best knowledge, not a licence. Also: no known restrictions. ### NASA media guidelines NASA's rules for its images: generally not copyrighted in the US, credit NASA, don't imply endorsement, don't use the NASA insignia or logotype, and ask before using identifiable astronauts or staff in ads. [Using NASA images](https://image.shep.bot/guides/nasa-image-rules) · [reference](https://www.nasa.gov/nasa-brand-center/images-and-media/) ### Licence verdict Image Asset Server's one-word answer to 'can this be used commercially?': yes, yes with credit, restricted, needs a paid licence or releases, unclear (check the terms) or no. Decided the same way for every source. [Image licences explained](https://image.shep.bot/docs/licences) ### Uploader-asserted licence A licence chosen by whoever uploaded the file, which the site does not verify. Such licences are capped at 'check the terms' here. ## Tools ### Image set The images one page, deck or post needs, one per slot (a hero, three icons, a background). The image set builder picks one image per slot with alternatives and writes the credits. Also: slot list. [Image set builder](https://image.shep.bot/build) ### Figure and caption HTML's
and
elements: the natural place for an image's credit line on a web page. credits.html from the image set builder writes them for you. Also: figcaption. ### MCP (Model Context Protocol) An open protocol that lets AI assistants call tools on a server. Image Asset Server's MCP endpoint gives agents search_images, get_image, build_image_set and list_sources. [Coding agents & MCP](https://image.shep.bot/docs/mcp) · [reference](https://modelcontextprotocol.io) --- Source: https://image.shep.bot/glossary