oops, sorry. Messed up adding pictures within the profile with pictures added to the signature.
I have not created a profile so I can just give some guesses: Did the filename appear in the dialog box? Is it smaller than 50 kB and of type jpg/png?
 Just tried myself; the picture is indeed disappearing. It does not matter if you use a local file or a link to a picture located on a http-server. Looking at the profile again the filename has disappeared from the dialog-box. Seems to be a feature not working... at least I don't see a picture when looking at my profile.
</p>Getting no work from Boinc...