Im having problems with the Preview app. I recently attended an Apple workshop where the trainer showed us how to add your signature to the bottom of emails etc. Basically you take a photo of a hand written signature using the Preview App. When opening preview a small box appeared with the instruction to hold up a piece of paper with your written signature on, then it takes photo and stores it as an image. But when i open up preview I either get the 'Finder' window opening... or this.. Any ideas where i'm going wrong please?