Sorry that I skipped a tutorial ^^' You are meant to buy the apple from the left side bar, and take photos of her when the skull is not showing. I'm not sure it will display correctly if you are not in full screen or if you monitor is small. I'm bad at ui ^^'
Over time you are meant to unlock more girls and a fruit tree to keep them happy.
Thank you for playing it, and grand of you to ask for clarification XD