Boolean logic - If image exists, then...

Occasionally when I open Windows Movie Maker an error message pops up on the screen. Therefore I need to instruct Sikuli to do something else in the event of the error message. Just that I am totally new to python and struggling with it at the moment.

How can I set up some sort of if statement as follows:

If (find this image), then do ABC.
else do XYZ.

Thanks!
Oh, and of course I can provide more information if necessary.