I’m trying to compare two pictures of the same area taken at two different times – but not being a great photographer, I was not standing in exactly the same spot both times, so I’m having to crop and zoom like crazy to get the before and after shots to match.
Let’s look at an example using two shots (one taken by Joe Ravi, CC-BY-SA 3.0; the other from http://www.metrodcpohtography.com) of the Jefferson Memorial in my home town, Washington, D.C. In this case I have both pictures in a PowerPoint slide, side by side:
Once I get them sized relatively, though, I might realize that I want them both to be bigger on the canvas. Fine, except if I’ve finally sized them both perfectly compared to each other, and I try to make one larger, I’ll have to make all of those minute adjustments all over again… or I would, if I didn’t make use of the group tool!