I've started to print my eQSLs as photos using the Amazon Prints service (only 9 cents for 4x6 photo prints, and you can get larger sizes as well). They are a little picky about the images, first of all they have to be JPEG format, no PNG or GIF images are allowed. And second, if the image is not a 4x6 aspect ratio, they will crop off parts of the image. That might be fine for regular photos, but is definitely not what you want to happen to eQSLs.
So I wrote an app to automatically add a border to images as necessary, so they are the correct aspect ratio for whatever size you want to print out. You can select a fixed color (black, white, yellow, whatever) or the app can pick the most common color from the edge of the image, and use that. Plus it saves it as a JPEG. You can process one image manually, or point it to a directory and it will convert every image file it finds. Much much easier than trying to do this by hand.
I have a beta version of the app here, it is available for Windows and macOS:
http://www.blackcatsystems.com/software/automagic_photo_image_resizer_app.htmlGive it a try, and let me know what you think.