This issue came up in discussions recently.
My understanding of the guidelines for image cropping is that the image should be cropped as close as possible to its edges, but not into the area of the banknote. Thus, no areas of the note would be removed. Many notes, especially older ones did not have straight cuts on them.
So, the question is, should the picture of the banknote be cropped so that the full image of the note is shown as in pic 1a or pic 1b below, or should it be cropped to cut off part of the image so that all edges are smooth, as in pic 2, bearing in mind that part of the image data is lost.
Discuss :)
pic 1a [with black background]

pic 1b [with white background]

pic 2 [cropped into edges]

