update: strip EXIF data from all JPEGs

update: strip EXIF data from all JPEGs

EXIF data can be abused to exploit systems a lot easier than the JPEG image
data can.  The F-Droid ecosystem does not use the EXIF data, so keep things
safe and strip it all away.  There is a chance that some images might rely
on the rotation to be set by EXIF, but I think having a safe system is more
important.

If needed, only the rotation data could be saved.  But that then makes it
hard to tell which images have been stripped.  This way, if there is no
EXIF, it has been stripped.  And if there is EXIF data, then it is suspect.

https://securityaffairs.co/wordpress/51043/mobile-2/android-cve-2016-3862-flaw.html
https://threatpost.com/google-shuts-down-potentially-massive-android-bug/120393/
https://blog.sucuri.net/2013/07/malware-hidden-inside-jpg-exif-headers.html

The big downside of this is that it decompresses and recompresses the
image data.  That should be replaced by a technique from jhead,
exiftool, ObscuraCam, etc. that only strips the metadata.