It's not just a question of image size (100x100), there's also a limit on file size (20k). So even if your image is 100x100 pixels, it might be saved with too high quality. You usually can't tell the difference with that small of an image anyway, so just lower the quality of the jpeg (assuming that it's a jpeg). If you don't know how to, flip me an email with the image attached to [email protected].