You need to follow some simple rules in order to get the Box Art to work on the USB Loader GX.

Disc Cover Image
The Wii Disc Cover Image will be place in the SD:/images/ by default and you can change the custom path if you are an advance user. The images must be in PNG format and not any other picture format.
The image size must have a dimension in multiple of 4. I will elaborate further seems this has confuse many Wii users. Lets say the Image size is 160 X 236. This is acceptable as both 160
and 236 divide by 4 will give u a whole number and that means they are
a multiple of 4. I hope all of you get what I mean.

DVD Disc Image
The Wii Disc Image need to have a resolution of 160X160 and must be place in SD:/images/disc/ and you can change the custom path if u are a advance user.