I started making Photoshop type edits after I was here for about three months. You want to find/make .png files, with a transparent background. Grumpy Cat or Doge head for example. You can add them to your creations using the add image button in imgflip and move/size them like the scumbag hat. I use an Android app called Eraser to make most of my png files.
I can't take credit for the Picard with gun one, a user contributed template from a couple years ago. I think I found it by clicking a tag and scrolling through the results. imgflip.com/memegenerator/47096792/U-wat-m9