This project started out as a simple tool for using the iTunes Search API to download 600x600px artwork for TV shows. However, it became a lot more popular than I expected and requests were made to add movie and iBook artwork. I've added these in addition to incorporating album artwork and app icons from the App Store.
To find artwork, simply type the name below and choose the media type and country from the dropdowns.
I've included two links at the top of each piece of artwork; standard resolution and high resolution. The standard resolution will generally be 600x600px and is the size that is displayed inline. The high resolution can be anything; I've found instances of movie artwork at 1600x2400px and TV shows up to 2400x2400px. However, the high resolution does not always work, particularly for iBooks, Movies, and Albums (albums are now working thanks to a tip from John Leustek). It seems to depend on the country and studio involved but you generally need a special key to get that high res artwork and you can only get that key by purchasing something from iTunes (and then it only lasts a short while). With app icons, there is only one artwork link (click on the icon). It will either be 512px square or 1024px square depending on how recently the app developer released or updated the app.
This tool is provided completely free of charge. If you found it useful, please consider downloading WallaBee, my free iOS collecting and trading game.