Still Images and Premiere Pro

There is a lot of good info for this here from Adobe.

In this case, our video images are 640 x 480 pixels. How do I know?

I select a video clip on the timeline, and go to File> Get Properties For > Selection (or hit shift-command-H) and see my Properties.

So, if I'm making slides in Photoshop, or resizing them, I know the exact pixel dimensions to use.