That basic idea is roughly how compression works in general. Think zip, tar, etc. files. Identify snippets of highly used byte sequences and create a “map of where each sequence is used. These methods work great on simple types of data like text files where there’s a lot of repetition. Photos have a lot more randomness and tend not to compress as well. At least not so simply.
You could apply the same methods to multiple image files but I think you’ll run into the same challenge. They won’t compress very well. So you’d have to come up with a more nuanced strategy. It’s a fascinating idea that’s worth exploring. But you’re definitely in the realm of advanced algorithms, file formats, and storage devices.
That’s apparently my long response for “the other responses are right”
As others have noted, the app doesn’t work on mobile yet. Anybody willing to share the content here for mobile users?