This picture should not show up. If it does, your firewall allows WMF files
There are currently exploits circulating for a purported zero-day vulnerability in the component in Windows that handles Windows Meta File (WMF) graphics files. One way to prevent falling victim to this type of attack is to use your firewall to block those types of files. Ideally, of course, you should never block at the firewall, but rather only allow; allow that which you know is good. However, if you are in a hurry to get something done, enumerating all the known good things is fraught with complications and probably would lead to blocking things that you do really need, with associated work-stoppage problems. Unless the world is melting around you, you probably do not want to run that risk, so in the short term, just blocking a few things is not a bad idea. It is also difficult though. For instance, I am not aware of whether only WMF file handling is affected or whether EMF (Extended Windows Metafile). I blocked both just in case. For instructions on how you can do this with Microsoft ISA Server see Jesper's old blog.
There is a plethora of information on the web about this exploit, such as the following: