In addition to what CTho9305 said, if you're running WinXP (maybe w2k also?), go to windows > system32 > drivers > etc > look for file with no extension simply called "hosts". This file may or may not be there, and may or may not be empty; it's a simple method of making your PC think certain domains (i.e. known advertiser ones) are located on a IP which is actually pointing at your own machine. Entries usually look like, for example:
127.0.0.1 doubleclick.net
Open with notepad and see if the domains where these pics are from is in there. If so you can delete that line if you want.