Guides
Glossary of image and licence terms
The words you meet when you look for images, pick a file or read a licence, defined in a sentence or two. Each term links to a guide or a collection where it matters, and has its own address (for example /glossary#cc-by) you can link to.
Images
- Stock photoalso stock image, stock photography
- 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.Search free imagesFree images for commercial use
- Public-domain artalso open access art, museum open access
- 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.Museum open accessImpressionist paintings
- Botanical illustrationalso botanical plate
- 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.Botanical illustrations
- Ukiyo-ealso woodblock print, Japanese print
- 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.Japanese woodblock prints
- Archive photographalso historical photo, vintage photo
- 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.Vintage city photos
- Iconalso icon set, pictogram
- 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.Free SVG iconsSVG icons and transparent PNGs
- Illustrationalso clip art, vector 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.
- Texturealso background texture, pattern
- 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.Paper textures
- Composite imagealso false colour, representative colour
- 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.Hubble and Webb images
Image files
- Resolutionalso pixel size, dimensions
- 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.
- Megapixelsalso MP
- Width times height in millions of pixels. A 6000×4000 photo is 24 MP. More megapixels allow larger prints and tighter crops.
- DPI / PPIalso print resolution, 300 dpi
- 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.
- Aspect ratioalso 16:9, 3:2, 4:5, 1:1
- 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.
- 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)also SVG, scalable vector graphics
- 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.SVG icons
- Raster imagealso bitmap, JPG, PNG
- 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.
- Transparent backgroundalso alpha channel, cut-out, PNG transparency
- 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.
- TIFFalso TIF
- 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.
- IIIFalso International Image Interoperability Framework
- 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.Reference
- Resized copyalso rendition, derivative
- 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.
- Originalalso master, full resolution
- 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.
- Alt textalso alternative 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.
Licences and rights
- Public domainalso PD, Public Domain Mark
- 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.Free images for commercial useReference
- CC0also CC0 1.0, public domain dedication
- 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.Reference
- CC BYalso Attribution
- 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.How to credit CC BY imagesReference
- CC BY-SAalso share-alike, 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.Reference
- NC (NonCommercial)also CC BY-NC
- 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.Reference
- ND (NoDerivatives)also CC BY-ND
- 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.Reference
- MIT, Apache 2.0, ISCalso open-source icon licence
- 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.Reference
- SIL Open Font Licensealso OFL
- 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.Reference
- 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 usealso editorial only
- 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.Free images for 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.
- Attributionalso credit line, TASL
- 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.How to credit CC BY images
- Rights statementalso no known restrictions
- 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.
- 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 imagesReference
- 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
- 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 setalso slot list
- 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.Image set builder
- Figure and captionalso figcaption
- HTML's <figure> and <figcaption> 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.
- 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 & MCPReference
More depth in the guides and in image licences explained.