Adjusting Scale and Placement
Scale matters. Once you’ve added source images to a composite document, chances are good that you’ll need to scale one or more layers (and possibly transform them in other ways as well) so the content appears to have the correct proportions relative to other parts of the image. Using smart object layers in combination with the Transform tools is the easiest way to achieve good scale, because they allow you to make more than one attempt (at different points in the compositing process if needed) to get everything just right.
If you scale a smart object beyond the pixel dimensions of the original photograph, you ...