I get letters all the time asking how to make parts of an image "invisible" or transparent. So many times someone puts an image on the their page and it looks great until the background comes in. Then the little icon reveals itself to actually be square rather than round. Oh, the humanity! Yet on some pages, you can see right through the image to see the background. I use to think the person went in with an image program and simply cut holes with the crop command. Don't laugh...it seems plausible.
There is no cropping going on at all. The person who provides a transparent image has simply run the gif (Yes, it has to be a gif) through a transparency program, highlighted what he/she wanted transparent, and saved the image again in a special format called "GIF89a".
Here's Neil Murphy's description of the GIF89 process: It's named GIF89a because the GIF format was standardized in 1989. The Transparency was the second part of the list of standards, thus the "a".
There are a ton of them on the net. You can head to Yahoo's Image Transparancy Page. There you'll be able to surf for a program of two. I'm sure all the programs that come up are good, and I couldn't possible attempt to explain how they all work right here, so I'll only go over two: Paint Shop Pro and LView Pro. I use them both.
 Paint Shop Pro |
 LView Pro |
| Grab the Program Here | Grab the Program Here |
| Transparancy Tutorial | Transparancy Tutorial |