As far as avatars go, here is the key...
Your avatar will be SQUARE, so if you try to link to a rectangular image (most images are rectangular, not square) it will be stretched to fit the new dimensions! In other words, the height/width ratio will be changed and your pic will look whacked out.
Your avatar will end up displaying as 65 pixels wide and high.
The absolute best way to handle it is to:
1. Open an image in Photoshop.2. Crop it so that it's square.3. re-size the image to 65 x 65 pixels. If you don't re-size in an image editing application, the message base software will do it for you, and the results can be...unpredictable.