I also get the pictures, which I like, BUT I also get, from time to time, the problem that Leeneia describes, where the whole thing gets firmly stuck on the picture, and try whatever I might - any key, escape, left click, right click, it just will not budge. So, that means, as she says, you cannot get to the log in box, and the only way to resolve it is to do a crash shutdown and re-boot. The computer plainly doesn’t like this as it takes ages to re-boot after such an incident.
For me, it doesn’t happen during initial boot-up, but mainly if the computer has been in “sleep” mode and I then go to waken it up again - usually just when I most urgently need to use it!
Will try what Peter L suggests, as it’s a frigging pain!