Remove personal data from photos before sharing them on the internet
codepo8.github.io
codepo8.github.io
Even better, it should have some sort of self-checksum of the entire file, so it is harder (but not impossible, unfortunately) to extend the format beyond the original spec.
This would make it far simpler to encourage better behavior: the average person isn't going to bother if you tell them to run exiv/exiftool. Instead, saying "Normal image files are not safe! Only upload $SAFE_FORMAT files!" will get at least some people to strip the files, and those that don't should at least get a more useful sense of what is safe/risky.
In the (very hypothetical) future, once the format was used, it would even be possible to for browsers to explicitly deny upload of JPEG/PNG/etc or they could auto-convert other formats.
Security doesn't work when it relies on complicated methods that won't actually be use in practice, so changing the format of stuff that is used might be necessary.
[1] the same idea would obviously apply to audio/video/whatever files
cp files-to-strip /tmp/foo
exiv2 rm /tmp/foo/*