Here is a quote from the readme
This is where your covers are located, if you cannot view covers from within the loader then you are doing something wrong. It is best to download covers thru the loader using wifi.covers:
If you cannot do that just download 2D covers and ad them to the covers folder, you may be confused because there are also other folders in the covers folder. There are example cover images in each of the folders so you can see where to place each type of cover image.