If you have a few images that you really like and want to use you can just select and add those to the portraits/bodies folder and use them in-game manually. If on the other hand you have several images you could just use Kyler2's Improved Random Portrait mod and use the 'Random Portrait' button to change between fitting images without having the need to make the game load all images and become slow or potentially crash. I bet you are not aware of this mod yet so I highly advise you to check it out.
Viewing post in Potrait/Bodies problem?
I am but thanks anyway! I thought about this too. Just trying to have good random potraits, but welp i have many packs which i fused, and after that i deleted copies so idk how it will be working with this mod, or with using both bodies and portraits. Sadly not everything have same name :/ But thanks anyway! Still im trying to defeat this errors but i dont know how to use this pngcrush... :/