The Wallet Size Prints consist of 4 images with the same photo. They are delivered as one big print, and still have to be cut out by yourself. The size of each single wallet print is approx. 5 x 6,5cm.
Your image file should have an aspect ratio of 3:4 to correctly print the images. Other aspect ratios could cause a loss of parts of your image.
Find more information about aspect ratios here...
The recommended minimal resolution is 192x148 pixels.
The manufacturing tolerance is 1-3mm per side. Due to manufacturing tolerances we recommend to place texts and important parts of your image at least 5mm from the border.
Source: http://www.pixum.no/service/14998-information-and-tips-about-the-wallet-size-prints.html