Yes, I have worked with panels on occasion. And they are not always what you would expect them to be.
Not only are the pictures not the same size, they are not actually square either. This is why in the quilt I'm working on the pictures are framed by some of the Fizz fabric. Once they were framed, I could cut them into a 6 1/2" square. And now they work in the quilt.
By the way, the pattern we used is called Baby Four Patch Free Crib Quilt Pattern, and it is available from the Fat Quarter Shop. The use of the panel was a choice we made. It is not required for the pattern.