Simply launch the program, point to an item in Diablo 3 and press F1. The item popup is automatically detected, cropped and captured. This also works for items anywhere else on the screen, such as items on the ground or linked items from the chat.
Clicking on an item in the list removes it. Hovering over an item in the list will show a popup with the stats, much like in the game.
The Collage button (or pressing F2) will create a numbered layout of all captured items and save it to your Pictures folder. An example can be seen here.
Since v0.2 there is an automatic check for updates which will prompt a notification if a newer version is found.
Better not look at it, it's horrible right now.
This code is released under the MIT license. See LICENSE.