Comment 9 for bug 1445755

This happens if someone inserts a flash card or copies a collection from some other music library, such as iTunes. For songs that don't have embedded artwork, various music players store the artwork in a file inside an album's folder. iTunes uses AlbumArtSmall.jpg and Folder.jpg. Other players use cover.ext, album.ext, album art.ext, .folder.ext, or folder.ext (where ext could be png, jpg, or jpeg).

It seems that gallery app shows these files as if they were photos taken with the camera app.

For a test case, drop an image called AlbumArtSmall.jpg or cover.jpg into a music album folder somewhere. I believe you'll find that image in the gallery app then.