your sigpig definitely is a square though and a .gif as well, not a .jpg it has an image surrounded by transparent pixels, which you obviously don't see, but it is a square. Any image you'll find on the web will be a square.

If you want to save an image with a visible circle and the pixels outside the circle, that fill up the square, transparent; you'll have to make a .gif or a .png file (but keep in mind that Internet Explorer doesn't fully support .png files ).

If you use Photoshop and have a file you want to save with transparent pixels, make sure that you have at least one layer on top of the background layer. Make the background layer unvisible (uncheck the 'eye' in the layers window) and you'll see the grey/while checkers pattern, which are in fact the transparent pixels. On top of the background layer, make another layer with the part of the picture you want to see (ie. select it and copy / paste it from the file you want).

THen you should see your image surrounded by the grey/white checkers board pattern. Go to file>save for web; select GIF on the right and make sure transperency is checked. This should save your image with the transparent pixels and makes it looks like it's not a square image on the web.

I'm not sure if this explains it to you... kinda depends how much you use Photoshop as well...