Yes, there is a way. I do it using Visual Logic. First of all, I have a quad that doesn't have a material assigned yet, and it's centred on the scene. For some reason, I have it with a width of 1 pixel and height of 900 (that's the max height I want, but I can't remember the reason for the width being 1 pixel because my max width is 1600). Those dimensions probably don't really matter with the Visual Logic setup I used. Then I have the quad set to auto size only on material assignment. The visual logic handles the sizing of the images so that they fill the max dimensions I want without being distorted.
See the attached screen shots for details. Please note that my picture scenes have an optional title, hence the selection box at the top left. This is also on XPression PRIME 6.5.
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