The image you want to overlay onto the magizine is retangular and the magizine is not as it is photographed at an angle.
Therefore you will have to use Edit/transform and probably distort to get it to fit.
Curt is corect about the distortion but I would give Free Transform a try.
Open both images in PS and move the new image on top of the original. I would Ctrl T to get to the transform box. Hold down the CMD button and click on a corner of the image you want to put on top the original one and drag it to the proper corner. Do this with each corner. You will have a larger file to look at but take a look and see if the distortion is too bad.
You might also look at using Filter>Vanishing Point.
If you go to this page: http://russellbrown.com/tips_tech.html, look down under
Russell Brown Presents: Things You Need to Know
you'll see Text in Perspective with Vanishing Point (same applies for images).
more on vanishing point: