Please see
viewtopic.php?f=4&t=718&p=2686&hilit=resource#p2686In short, DSL dictionaries do not hold any sounds or pictures in them. It's a simple text file. Your dsl file is not compressed that is why it is 500MB.
Image and sound resources can be zipped into a file with the name foo.dsl.files.zip which should be put next to the dsl file. DSL file can be compressed with dictzip (foo.dsl.dz).