Hmm, I think you would need to hack the code to use the operator picture instead of the live help picture. I can do a search in code for it and maybe post a file for you, however it won't be until later today (it's 1:30am here, and I'm off to bed!
Been laying in bed thinking about this... I think it could be done with some minor changes to the /live/icon.php file, and I believe it would require some calls to find op, get the picture, and serve that picture instead of the department icon. Probably the most elegant way is to have it serve a default picture if the agent's pic is missing. I have use for this mod as well, so maybe I can slip it in with a config option. Additionally, I don't think it's going to take much to make it happen, just a few lines of code and one configuration variable (basically a switch).
One thing to keep in mind, if you do this, you will want the op pictures and the offline (as well as default picture) to all be the same dimensions to keep it from breaking any theme you might have on the page. However, this is easily done with just about any photo editing software out there.