[schtono]

First: I wonder if all jpeg viewers accept the "new file", I guess some will choke on the altered files.

Second: If this works it might be possible to distribute hidden files through profile pictures (one facebook and friends) :) I'm glad I never store original jpegs in my web projects, but rather saved processed versions (resized etc).

[viraptor]

1. Most of them work, yes (especially all browsers).

2. Bookchan uses that method to distribute ebooks. People simply post the book cover picture with the ebook attached in .rar on an imageboard. (eg. http://bookchan.wikidot.com/mario-puzo)

[nirmal]

This works most of the time because jpg files are decoded from the first byte until the last byte of the image. Any bytes after need not be inspected. Zip/rar are decompressed from the last byte going backwards. Again stopping as the final byte of the archive is seen.