I recently modified my photo booth to now post one image to Flickr. I used a Raspberry Pi B+ and a single button. A nice simple experience.
See the code here: https://github.com/drumminhands/drumminhands_piFlickr
Here is a quick picture of the hardware plugged in.
Note, this diagram shows the LED and large button separately, but really the same button has four wires connected to it: two for the button and two for the LED. Also, the button has a built in resistor. The small middle button exits the program so that you can edit code or settings as needed. Hide this button from users.
Thanks to SirMo76 for the cover photo.