If they're internet ones then I would say it is not unusual. Each new image you see on a webpage by default is cashed and saved as temporary files. For example if you load a thread with 40 posts all from different users your PC will save all 40 of their avatar images, plus any other images you see, etc. It all adds up over time.
You can disable this but it helps load web pages faster. But deleting them every once in a while is good to speed things up a tad and mainly free disk space.
I had over15,000 on my desktop pc before it decided not to work which was yesterday.
But the ones I am talking about are in %userprofile%\appdata\local\temp