The iTunes store is a good source of high-quality album cover art. If you search for the album on Google Images, then visit the page and right-click on the cover image, you will get a 170 px by 170 px image. Change the 170x170 in the URL to one of the following values to get a higher resolution image:

  • 64x64
  • 100x100
  • 170x170
  • 340x340
  • 600x600
  • 1200x1200
  • 1400x1400

Alternatively, use this handy webapp to query the iTunes search API and get to the source image directly.