The templates are setup so they will assume the image is going to be the "page name + .png" . So all you need to do is upload a file that has the exact (case sensitive) name as the monster. Eg: Lloigor_the_Crazed.png (use spaces in the actual file name on your computer - it will automatically add the underscore when you upload).
I've been using some of the screenshots from another thread to give a face to some of the Unique monsters that can be encountered in the Beta. If you happen to stumble upon more please feel free to upload cropped images to our wiki. Here are some guidelines for getting a good shot:
- capturing the title/health bar of the monster is not important
- avoid getting the cursor in the image
- monster shots should be taken without the red "mouseover border"
- try to get the front facing of the monster
- shots should be taken in highest video settings at 1080p
- all the better if you can capture them doing something interesting