Hi, if you have no file size concerns you can use your image as it is, just making sure it's in a format recognized by PowerPoint - such as JPG. You insert the picture to PowerPoint presentation, set the image size there and that's it.

If you have concerns over file size (and assuming your original picture is of high resolution), you could scale the resolution down in Photoshop but would still have it well exceed your max. screen resolution since PowerPoint still need to scale the image file when displaying it.

Hope this helps - unless I misunderstood what you were asking.

Petri