I have the same issue. Someone sent me some pictures in an email and I viewed them. I have no reason to keep them around, but I can't delete them. If I go to the main email screen->Browse Files->Recent Files or Pictures->Other images, I see the files, but no way to remove them.
Ive had the same problem.. The only way i know to delete them is to take the micro sd card out of your phone, insert it into a micro sd card adapter and use a micro sd card adapter usb that plugs into your usb port on your computer. From there, you can go inside the micro sd card, go to the recent files folders and delete them.