webMAN MOD, IRISMAN and multiMAN are 3 different homebrews.
Although they share some rules to detect the covers, they have significative differences in the way the covers are found.
If I recall correctly, some of the rules shared by the 3 backup managers are:
1- Get the cover from the same folder of the ISO. e.g. Filename.ISO & Filename.JPG (or .PNG)
2- Get the game ID from the file name (only some file name formats). e.g. BLES12345-[Title].ISO
Placing the cover images in the folder PS3ISO with the same file name of the ISO should be the best method accepted by all these homebrews.