Update: I think I should explain this a little better.
The web browser will think that getpic.pl is simply a directory, and that
what it is accessing is a file called bobo.jpg. If you return the right headers, the browser will think
that it is retrieving a static jpeg. Depending on how the browser determines whether or not to reload the picture, that may be all that you need.
On the other hand, some browser will request the files headers in order to check modification time, file sizes, and whatnot. You need to be prepared to fake those headers if necessary.