Board Thread:Support Requests - Designing Your Wiki/@comment-38546904-20190311225642

I had tried searching for nearly two hours to find out how to do this, but unfortunately I just cannot find what I'm looking for. I'm sure this Wiki has seen this question many times, but how does one go about uploading a custom image to fit the FULL background of the wiki (like the background of this). Also, does anyone reccomend any image compression programs so that I can resize the image without dimisnishing quality?

This is the image I'm using: 