On ASys DataService's blog, there's an article posted about creating rounded corners on your images with a little help from the PHP GD libraries.

I needed to add rounded corners to some pictures and didn't want to modify the source files in Photoshop (I think it's a bad idea to modify original pictures if the effect can be added dynamically).

That's when I decided to use the GD library, which I had found very useful in other projects. I'm not saying that this solution is perfect or better that others, but it has worked very well for me, and I hope it will be useful to some of you as well. Feel free to contact me if you have any comment about this code.

He briefly describes the code, noting where you can make config changes based on your needs. After that, it's all code, a procedural script that takes in any file and spits back out a custom rounded-corners image with your chosen settings. He even gives a PNG file of the rounded corner to use...