HP's Sprocket Photo Printer is about the size of a deck of cards, making it easily portable. It has an internal battery, so there's no need to always print near power.
Of course, you'll need to charge it first via the Micro-USB port. I powered it via my computer, but you can also connect it to a USB wall plug (not included).
Next, load the wallet-size photo paper (you get 10 sheets in the box). Peel off the back of each sheet to make it a sticker.
You control the printer through the free (iOS and Android) Sprocket app. You can print straight from your phone's camera roll or connect to your Flickr, Facebook or Instagram accounts.
After selecting a photo, you can print it immediately or edit it with a variety of effects like borders and text.
Printing each photo takes about 40 seconds.
Print quality isn't great, but for what it's designed to do, the Sprocket performs well.