Patch is a modification of the source code - here Rockbox. To use AlbumArt WPSes effectively you need to have a build (version) of Rockbox supporting it (using this patch).
I've finally found the thread you were asking for help with installation:
http://forums.rockbox.org/index.php?topic=5951.msg46124#msg46124but we still have no idea what version you use.
"Official" versions: 2.5, CVS daily build and "bleeding edge" build don't support AlbumArt feature - they don't contain the patch.
To use AlbumArt you need to:
- compile your own Rockbox with the AlbumArt patch added (what is obviously beyond your competences)
or
- use one of the builds which the great guys like Senab, Josh or beloved PJulius offer. They are ready to use.
Anyway, AlbumArt is experimental and delivered not by official developers but by some Rockbox users. If you have a build supporting AlbumArt - try some different one, maybe that was an error in the build.
If it's not working - read the documentation how to use AlbumArt or try to get some help from its developers.
More information you will find in the
Unsupported builds section.