first of all, thanks for updating. But i have one last suggestion:
You can search for quadratically pictures like i discribed here:
Then you'll be sure you will find a cover. Its to avoid that you'll find pics which are not the covers, because covers are always quadratically!
And it would be great if i can search the other pages of the google results if its possible, because i've had one titel which only got low resolution (80x80 etc) in the first google page, but in the second a found a good resolution (600x600)