You can scan your photos into your computer. Or, if you now have a digital camera, I've found that sometimes just taking a new digital photo of the previous print you had might be better.
In any case, once you have it on your computer, you need to correctly size it to meet DISboard standards. Go to the Tech Support board and read the section about signature guidelines. There are samples there.
If you don't have any photo processing software, you can reduce photos using Microsoft's PAINT program. You'll find that program under the ACCESSORIES grouping on your computer. Open the photo and use the feature to change the aspect to reduce the photos.
Once reduced, you then upload the photo to a hosting site somewhere. Photobucket.com is a free, popular one.
After the photo is uploaded, simply link to it in your signature.