How would I go about making this project?

Hello,
I am inquiring if this would be a possible project, and how to go about making it: Basically I am interested in hacking a printer so that every time someone makes a certain gesture, a picture is printed. I currently have an Arduino Uno and know the basics of using a photocell, but that is about it. Any tips would be greatly appreciated!
Thanks

Hard part will be seeing the gesture.
Mimicking the serial data to a printer is not too hard.
If it's a USB interface to the printer, that will add hardware complexity.

Do you have any idea about what parts I may need?

Use a PC to control the printer - then your problem is just to run a command on the PC to print a file when the gesture is detected. I don't know how you plan to detect the gesture, but if you're thinking of using image processing techniques, the PC would be the platform for that too.

I wasn't particularly set on a gesture. I was considering using sound as well, or even a relay.