A rule of thumb the adsense team mention is would you feel comfortable viewing the material in a workplace environment? If not, then it should be fine.
Here is my rule of thumb, if you have to ask if it's against the TOS then it most likely is. Considering all the copyright issues and such with those type of screensavers there any many different violations of the TOS.
the problem here is copyright i had the same problem and i didnot use adsense do u have the copy right for these screen savers if u do dont worry
I don't see the problem if its not over 18 material so long as you have copyright as others have mentioned.