I don't know ... that sounds like a pretty rare edge case.
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.
People often have collections of images that are kept in rars or zips not for compression (which as you say this is no good for) but for convenience and organization. Or consider e.g. the "cbr" pseudo-format, where comics are stored as a rar of images, one per page. I can well imagine a web-based CBR viewer.
I'm sure there are other use cases, but that one immediately comes to mind.