After straightening (or levelling) in my opinion the second most useful tool is the crop tool. Often the must be used together to trim off the little blank triangle around the edges. In fact most newer software either does that automatically or gives a fit option in the cropping. However trimming up the edges is not the only reason you should crop and I will talk of other reason in future posts. The cropping tool in picasa dates back a long time but it is very easy to use and has two important features. The first is that it is interactive and it show the area to be trimmed off greyed out. So you can judge what you are removing. The second is it offer both a freeform (manual) mode where you can stretch out the bow to any size elongation you want as well as fixed ratio crops so that the cropped image will fit certain paper or screen sizes. In this second mode the cropping marks will expand or contract in both dimensions to maintain the selected ratio. The recent version of picasa even give you three example crops and you could click on the most suitable. In this example I'm trimming up the edges on a hand held multi-image panorama for I’m using the manual trim.