I've finally got around to making sure each song on my iTunes has an album. Now I want to put the album art with the song. I know there are album are importers, but you can only do it album by album, one at a time. Is there one that I could just select every song in my iTunes and have it put the correct album cover with it?
Shift+left click to select all the songs on an entire album, then right click on the selection and click "Get Info". There's a little box on the right side of the window that you can paste an image.

I usually copy and paste my art from Google Images.
Oh, whoops. I didn't answer your question.

I don't think you can do what you want.
You could do the select all method, or just do it manually. Theres no way itunes can recognise certain jpeg files and relate them to an album computers dont work that way :P
Ctrl + A to select all, then go Advanced > Get Album Artwork.

It'll take a while if you have a lot of albums, and it will get artwork so long as the album+artist names are identical to those in iTunes store. I believe you also need an iTunes store account though, not certain.