[media type]=audio -[Image File]=[] [Image File]=.,\
this says, all audio files (obviously) but not those whose [image file] field is empty, and of the ones that are not empty, only show ones that contain a dot or a back-slash.
the exclusion here is probably redundant.
There's one other leetle problem scenario that this doesn't cover....
Say, for example, the [image file] field contains: C:\coverart\coverartfile.jpg
This track will be included in your search results.
If the path is no longer valid, because you deleted the file, or renamed the directory or something similar, MC doesn't deal with the situation very well.
It retains the invalid path information, and that is what gets displayed in the 'image' action window (the path) instead of an image.
Cover art can be a right royal pain in the proverbial at times!!