The thumbnail is part of the EXIF metadata. It's reasonably well-known now, but it was not always the case... http://graphicssoft.about.com/b/2003/07/26/techtvs-cat-schwa...

Huh, interesting. Thanks!

A few years ago a TV presenter got caught out by this, she posted a cropped photo of herself online, but the original, uncropped version could be recovered from the file which showed her topless.

There was a trend for a while of people posting images to imgur that had a totally different thumbnail. A rickroll of sorts.

I believe it's a Photoshop thing, rather than something common to all images. Photoshop in general does unusual things.

See also: http://u88.n24.queensu.ca/exiftool/forum/index.php?topic=451...

You can use 'exiftool' on Linux to manipulate the EXIF data, get rid of the thumbnail, or set it to whatever you want. Imagemagick's 'convert' command also has a '-strip' option that will get rid of all EXIF data including any thumbnails.