They may still be there, but someone would have to know how to find them, AND go looking for them, in order for them to be found.
There really is no sure way to delete anything on a hard drive, short of physically destroying it. Something along the lines of melting down the platters to nothing but goo. Otherwise, there's always a small chance someone could manage to get data off there.
The good news is, most people have no clue how to do this. Also, the more you use the computer, the harder it will be to recover those files. It's almost never impossible, but shouldn't take too long before you'd need the resources of recovery professionals.
Not to add to your paranoia, but memory cards for digital cameras work on the same basic principles as hard drives, and are also potentially subject to data recovery. So whatever these photos were of, if they are still on the memory card for the camera, probably best to make sure it's stored somewhere people aren't likely to go looking for it.
I downloaded some personal pictures from a digital camera. I deleted them as well as cleaned out my recycle bin. Are they completely gone? I don't want my kids to ever find them or the repairman if I ever have to take it in. If they are still hiding somewhere- how can I get rid of them?