This tutorial was created for Photoshop CS2.
Any other programs may or may not work. :D
1. Open up an image.
2. Click on the Rounded Rectangle Tool.
3. Make your foreground color black, if it isn't already.
4. Click the toolbar options so they match the ones in the photo below:
5. Now drag the file size so it is larger. Not the picture itself though. You may already be on maximized editing, so that works too. If not, an example below:
6. My radius is set to 220 pixels. The larger the number, the rounder the corners.
7. Drag a rounded rectangle over the image. Be sure to start at the very left top corner, to the very bottom right corner. Try to be precise. It looks cleaner.
8. Drag rounded rectangles over 3 corners now. Make sure it is all covered by black. It should look like below:
9. Next, go to your layers palette. Control & click each shape layer.
10. Now press control + e. Or go to Layer > Merge down.
11. Click on your background layer.
12. Press control + a, and then control + x. This selects all, and then cuts it. Or you can do this by going to the edit menu.
13. Now click on the shape layer. Press control V.
14. Set that layer mode to screen.
15. ALL DONE! :) Yay! Now you can merge all of the layers down, by control + shift + e.