Downsizing photos for including in a video

Steve's advice is always good.   But, my experience is a little different.  

With a relatively strong laptop with 16GB of RAM, I don't see any significant image quality differences.   I can use the original image of any size and not see any editing speed differences either.  In other words, I can skip the downsizing step.  

Unique in Premier Elements is the inclusion of Adobe Camera Raw (ACR) functionality.   RAW files straight from the camera import into the program.  Premiere Pro can't do that!  If a Lightroom Classic user turns on the feature to save Develop adjustments to a sidecar XMP file, Premiere Elements will read the XMP and the import will include the adjustments.   The files are big, but Premiere Elements does not balk.  

Although the program does a pretty good job of downscaling almost any photos, I've found I get the best results in my HD projects when my photos are no larger than 2500x1875 pixels in size. That gives a bit of extra resolution for a pan and zoom.

I also recommend that before you import your photos into Premiere Elements you first go to the preferences (under the Edit menu on a PC) and, on the General page, uncheck Default Scale to Frame Size. That way your photo will come in at full resolution rather than artificially resized to fit the video frame.