Issue album art image and ID3v2.4 UTF-8

If you see weir characters, you might want to have a look at this thread:

/t/2785/1
about problems with unicode characters.

Then, if you do not see pictures, it could be that they are too large. Some phones do not like pictures bigger than 200*200 ...
You would have to adapt the size of the exported pictures with an external program and then re-import the resized ones.