You don't just enter the URL of your photo (from your photo hosting website) to the thread. You need to key in -
And the URL of your photo can be seen from your webhosting site... you either move your cursor over it (which I always do) and right click on your mouse, then go to properties. Then you can cut and paste the URL of the photo to this thread using the abovementioned format.
It will be a bit more tricky with facebook account though... you might need to go to the 'download' option on your photo, and right click, then select properties then copy the URL from there.