Ok, so here's my problem. This is Bill:
Bill is a handsome dude, and his image is 400px wide (take note of the pink border). I can size him down to 300px no problem. At full size, he is 109px at his head, and sized down to 300, Bill is 81px. But now I have this image that someone gave me:
So now, the canvas size has increased, and Bill has some scenery, a snazzy balloon, and a...dog?
So I want to scale this new image down just like I did the original, but how do I scale the whole image down so that the box ends up being 300x300? I want the whole image to be there, and for Bill to be the same size as he was when I scaled down the original, so that when compared side by side with the original, Bill is comparatively the same size.
I am obviously generalizing here, but I run into this problem on a regular basis. It's not a problem if just the width or height has changed, because I can scale down based on the dimension that wasn't changed. But when both width and height have changed, all I can think to do is use the measure tool on a consistent part of the image (like the box or Bill's head), resize the image, measure again, and repeat until I get it pretty accurate.
Is there an easier, more accurate way to do this? I'm using Photoshop CS6.