You've fixed the problem but in case you are curious what the root problem is...
Picassaweb (sorry, didn't recognize the URL, makes sense now based on the google.com domain name), is sending back bogus MIME information in the header (shame on Google, they should know better). Other boards may ignore this information and look at the URL itself for extensions like jpg or gif to determine if it's a valid image URL or not, apparently the DISboard insists on seeing something like Content-Type:·image/gif or Content-Type:·image/jpg in the header.
Isn't Al Gore's interweb fun?