I don't believe you can currently crop a picture. If not, I want to request it.
I'd prefer the way you do in in Pagemaker where, after cropping, you can still click on the image and move it around as a greyed-image until you release it so you can, of example, play around with recentering it to get the best compositional balance within the cropped area. You can also take away part or all of the cropping from any of the 4 sides if required.
If you can't work out how to do that, then the dumber method used in MS Word would suffice. It's hard working with pictures without cropping.