Those stills are probably too large. Use photo editing software to decrease the resolution to match the output (e.g. 720x480 NTSC / 720/704×576 PAL. A little larger (eg.1000x750 NTSC) if you intend to do pan & zoom effects.
More details here: What resolution should my photos be in Premiere Elements?
Insanity is hereditary, you get it from your children
This ARTICLE might be useful in automating the Scaling of the images in the image editor, prior to Import into PrE.
I agree with Neale, that the Scaling of the images in PrE is probably at least part of the issue.
In case there are other factors, can you give us the full details of your AV Assets, your Project Preset and your Export/Share settings - just in case thre is something else happening?
I actually got it figured out. I had not rendered the timelime yet, but when I did so, my issue was resolved! Thanks so much!
Great news! Thanks for reporting your success.