FClintD, you have to make the decision of your final frame size in YouTube. If it's HD, like 1920x1080, it's wise to resize your photos to be roughly twice that size (that is if they are at least twice the size of HD to begin with). This will allow you to scale them up with less chance of losing resolution.
Down and dirty, I use position and scale keyframes for moving images simply around the screen. I like to animate the anchor point when zooming into or out of a specific location on the frame, though.
Chris and Trish Meyer of After Effects motion graphics fame prefer to animate the anchor point, usually. That said, it's much less fiddly to animate the anchor point in After Effects than Premiere Pro. I don't know of a way you can click and drag the anchor point right on the Program Monitor as you can in After Effects. I don't like moving the anchor point, and then the entire image moves. I'd rather it stay fixed.