Thousands of unknown files recovered!

I've just used Recuva to try and locate/recover some 'lost' photos. Without using the deep scan, I received:- [A:] 29,266 files found, 404,258 ignored. The majority of files were described as 'No preview available', however, apart from a number of recognised photos of mine, there were thousands of totally unknown photos, weird images, magazine pages, road maps, coloured boxes/patterns, etc., etc. Can you please explain how all these unknown/unseen by me files/images have been found in my computer hard drive? I should add that I have not actually selected any files to be recovered as the 'lost' photos have not been shown, presumably 'No preview available'?

The random pictures are web cache

The ignored files are the files on the hard drive that are not deleted

Sadly/Happily A preview or lack of one may not guarantee the chance recoverablility/unrecoverability