yet it still says "The URL you specified is invalid."
If you can post the entire URL you are trying to use for your picture here, we can help you.
If you did upload to your taxi profile and are using that image, first log out, right click on your profile image, copy paste that URL.
But before you upload any image URL to the forum acct, paste that same URL into a browser and make sure your expected image comes up. The hardest part of all of this is finding a place to host it. Second hardest part is restricting the size to 90x90 pixels or whatever the restriction is.
[The third 'gotcha' with images on the web can sometimes be in cases where the image is one file type, but has been renamed with another file type. For example, image.png gets accidentally renamed to image.jpg. You may still see the image on your computer, but some browsers choke on this kind of thing.]