Well done!
¹: http://www.rarlab.com/rar/unrarsrc-5.0.12.tar.gz ²: http://unarchiver.c3.cx/commandline
It is able to read headers and other metadata, as well as unpack files, but only if they're stored without compression: https://github.com/43081j/rar.js/blob/master/dist/rar.js#L54...
If I understand RAR, it actually uses a embedded virtual machine to specify the compression algorithm. That would have been the fun part.
I'm sure there are other use cases, but that one immediately comes to mind.
Photos you usually want to share are JPGs and 'raring' them doesn't do much good in terms of space saving.
The only image files you'd like to compress are those that are taking too much space (tiffs, raw images, etc). And if you take the extra effort to put them into an archive it's likely that they are taking up really a lot of space.
Thus it's very very likely that even one of those images is too big to upload it to the internet (tens of megabytes if not more) with today's common end user internet connections.
