Same as avatar requirements. Abridged version.

1. Must be a stock or free-to-use image. Shutterstock, dreamstime, unsplash, Pinterest, Google, other free "image sites", etc... are not considered stock due to prevalent art theft. A good source for stock images is Deviantart.
[Click to read more about stock images.]

***An exception to the above is:
- art you made, DID NOT TRACE, and is properly credited.
- art you have explicit permission to use and is properly credited.

2. No hotlinking. Upload your images to PostImage, ImageShack, etc.
[Click to read more about hotlinking.]

3. Human images are permitted with restrictions. It cannot be realistic art. Cartoons, silhouettes, chibis, yes. Photographs and portraits, no.

4. Must be credited to wherever you got it from or referenced from. A linkback to the original image is recommended. Examples include "#1234 on Wolfplay", "Username on Deviantart".
[Click to read Art Crediting Rules]

5. No AI allowed. Doesn't matter if you bought the adoptable from someone else or made it yourself, no AI allowed on WP at all.

For more info, review the stickies linked above and in the [Artwork Board].

If you do not know what a stock image is, or how to properly use an image, then don't use one if you don't want to risk your picture being removed.

Commonly Used Image Hosts: