Image Capture - what am I looking at?

[toothfairy]

 This is a screenshot from Image Capture. I understand that the large rectangle is the size of the area that is going to be scanned - but  what is the short horizontal line for?

[kvbarkley]

If I remember right, that is what it determines as another place you might want to scan as a crop.

[toothfairy]

Thank you for answering KV. I'm not sure exactly what the line function is meant to be used for - I wish the documentation on Image Capture was more thorough. I played a bit with the line and both ends of the line are "live" meaning that they turn red and can then be moved with the trackpad. From what I can ascertain, the handle on the line inside the rectangle is simply used to move the selection rectangle around. The handle on the outside of the line though, seems to be for rotating the selection area as shown in the screenshot.