As the FAQs to the right of this forum explain, you'll get the best results if you size your photos to no more than 1000x750 pixels and uncheck the option to Scale to Frame Size in Premiere Elements preferences (under the Edit menu).
For a similar Project, when faced with the different sizes and aspect ratios of images, I created a slightly abstract background, sized to my Frame Size. This was actually one of the landscape photographs of a lake. It was turned into a high-contrast image, and then effectively "Selinium-toned" to turn it into a duo-tone, i.e. shades of blue to almost black.* This was used as the Background for all images in Photoshop and each image was placed on it. This allowed the use of vertical images in the horizontal Frame. For horizontal images, there was a lot less of the background showing. It was constant throughout the entire SlideShow. With Keyframes for Motion>Scale and Motion>Position, I could Zoom in to portions of each image and Pan around them. As there was no Panning beyond that background, everything was sized to the Project's Frame Size, i.e. 720 x 480.
Here's an ARTICLE on resizing images in PS. If you went with the "background" idea, you'd just incorporate the additon of that Layer to the bottom of the Layer stack at the beginning of the Action.
Personally, I use a .PSD workflow and keep that all the way to Import. I always Save my working .PSD's, and then Flatten for Premiere. This allows me to go back and edit the working PSD, should that be necessary. For scans, I use TIFF and work at a pretty high resolution. I then scale these as is needed in PS.
The recommendation for 1000 x 750 is a good one, if one does need to Pan on a Zoomed out image - not too large, but not too small to Pan a bit. In my case, that was not going to happen, so I could limit all images to the Projects, 720 x 480. I also set the PAR in PS to 0.9, as this was a 4:3 Project.
* If you go with a constant background, you might want to start out with the full-color version of your choice and then transition to the "abstract" version that will be your background. That would let the audience know what it was originally, and they will be familiar with it, as the various images begin to appear atop it.
Thanks so much! You totally understand my problem and gave me just the direction needed. I already read the help section before posting originally. You're right that sizing things that way for a pan and zoom would not work in this situation. I love the idea of a constant background of some sort, sized to the frame size. I have lots of photos that are portrait style, squarish, and non-standard. It makes sense to save the work in psd format so the original files can be edited. I'm not sure how to flatten the images in Premiere only, though. Are you saying that if I flatten the image in Premiere that the original psd will be preserved in PS?
Again, your response was incredibly helpful. Thank you!
Premiere Elements will never change the original footage or photo. Any changes you make will only be reflected in the video you output from your project.
I'm not sure how to flatten the images in Premiere only, though.
The Flatten operation is one done in Photoshop, prior to the Save_As function at the end of the operation, or the Action. This is done from the Layers Palette via a little fly-out menu (upper left).
Now, I'm not sure of all of the handling aspects with PSD's in PE. In PrPro, one can Import a Layered PSD as a Sequence to keep all of the Layers intact. This is often done, when one wants to animate the individual Layers. I use this a lot with complex, Layered Titles. For general still images, I Flatten in Photoshop, and Save_As to my "Finals" folder. Then, I Import as Footage (even if there were Layers, PrPro would Flatten for me). I do not believe that PE can handle complex, Layered PSD images. I also do not know if it will automatically Flatten a Layered PSD. I'd just do this in Photoshop and be done with it. Remember, make sure that your Layered PS images are Saved separately, in their Layered form. One similar Project that I did, required that the old photographs be placed in a "frame" and also over a background. Into that Project, I realized that I needed to move the frame and the photograph around a bit. With the Layered PSD, it was so very simple. Had I only had the Flattened version, I would have had to start over, or break the components out, create more background to fill the gap when I moved the frame and the photograph. One Layered PSD can save hours of work.
I like keeping things in the PSD workflow. For my original shots, this RAW to PSD and then PSD all the way to video. I also like it when starting with a JPEG, which will have had some compression already. This saves having even more compression, should one go to JPEG again. In your case, I'd do TIFF for the scans, then keep PSD the rest of the way. Once you resize and Flatten, the PSD's are not THAT much bigger files, than a high-rez JPEG, and do not suffer from any compression artifacts.
If you go with a background from a photograph, rather than a complete abstraction, do consider a short animated section that will lead your audience to that background, which will then be used for all images and will be seen with all of the square and vertical images. I used a lake with a boathouse in the middle foreground. I did a long slow fade-in and Lighting Effect w/ Color Correction manipulation (to simulate a sun rise), and then a slow Cross-Dissolve to the "artistic" version of that photograph. I stuck in some SFX of morning birds, etc. and some mood music and had a 40 sec. intro so the audience could relate to the image used as the background for all of the rest of the images.
Good luck, and have fun with your Project,