If you have a recent version of Photoshop (and I think this applies to PaintShop Pro) and you try to scan in a $20 bill, Photoshop wont let you import the image. It also wont let you open a file of that image scanned by another application. The new digital copier machines will also prevent you from scanning currency.
How do they do that?
On the back of US currency (and other countries too), you’ll find little circles in a set pattern. On the $20, it’s a pattern of “20”. The arrangement of the “0”‘s is a set pattern that Photoshop is coded to scan for. If it finds that specific pattern of circles in the image, it considers that image to currency and it wont touch it. The post that I linked to goes into more detail will show you the pattern.
The new CS2 release of Photoshop now lets you open and edit currency images, you just can’t print them.