In most cases you can replace a broken image with some code that looks like this:
<img src="image.jpg" onerror="this.onerror=null;this.src='default.jpg'">
However, it doesn't seem to work with broken twitter profile images like this:
http://a1.twimg.com/profile_images/52087244/Photo_26.jpg
Is this because it is returning 403 instead of 404? Is there any way to fix this?