Adobe After Effects
Unless there is some aspect of this Pan, that I am missing, PrPro should be able to give you what you want.
I do this often, though in my cases, it's more like the viewer is on a trolly, passing in front of, say a long store front, or scenic panorama.
First, I determine how wide I want my still image to be. In Photoshop, I will Scale it to that horizontal dimension, and if I need only a linear Pan, will even Crop off any extraneous vertical pictures.
In PrPro, I then use the fixed Effect>Motion>Position, and Keyframe the location to match the view of the first Frame of that still image. I then go to the last Frame, and alter my Position to reflect that location, and add an ending Keyframe there. I might, or might not change the Keyframes from pure Linear, or might do Bezier to alter Velocity slightly.
Remember, one can ONLY view the pixels in the Frame Size at any one time. Imagine that we have a 16 x 20 matte, with an 8 x 10 aperture in it. Then, we have an 8 x 20 photograph, below that matte. Basically, we are dragging tht 8 x 20 photograph behind the aperture in the matte. At no time can we ever see more than 8 x 10, but over time, we can reveal the full 20" width of that photograph. That is what we are doing by animating the Effect>Motion>Position - dragging that still behind the "aperture" of the Frame Size of our Project.
Now, if there are many other attributes, that you would need to incorporate, beyond maybe some Zoom in/Zoom out, as the viewer "flies" over your image, gaining altitude, or lossing altitude, then AE would be the app.
The AEFX 3D Camera will allow him to "fly" and he can use a lot more resolution.