QUOTE(Wiki)
Sources List
The sources list allows you to use titleformatting scripts to specify exactly where Album Art Panel will look for image files. In order to learn how to use the sources list, let's look at an example:
$replace(%path%,%filename_ext%,)folder.jpg
-$replace(%path%,%filename_ext%,)*
--components\default.png
C:\Music\Arts\%artist% %album%*
--components\default.png
The sources list is organized into groups, based on which lines have a '-' in front of them. Each line that does not start with a '-' is the beginning of a new source group. A line which starts with '-' is part of the same source group as the line above it. In the example above, there are two source groups. The first source group consists of the first three lines and the second group consists of the last two lines.
The "Next Source" action (by default, left-clicking on the panel) will cycle forward through the source groups. Similarily, the "Previous Source" action will cycle backwards through the source groups.
The prefix "--" (two hypens) is used to indicate a "No Cover" image. A "No Cover" image is essentially a default image which will be shown if no other matches can be found. When automatic cycling is enabled, "No Cover" images will be skipped.
The wildcard '*' can be used in place of one or any number of characters and '?' can be used in place of any single character. For instance, the second line of the example above tells Album Art Panel to look for any file it can display in the same directory as the track. Album Art Panel will display the first image which matches the pattern. Characters in tags that are not allowed in filenames will be replaced with the '?' wildcard.
Album Art Panel will first look for an image at the location indicated in the first line of a source group. If the image indicated by the first line cannot be found, Album Art Panel will look at subsequent lines within the same source group and display the first image which can be found. If no image within a source group can be found, Album Art Panel will try to display the next source group instead. If none of the source groups can be found, the display will be blank.
Basically
Don't use after you defined one group, don't use a '-' for the next group
Here is mine