1) Make sure that your photos are no larger than 1000x750 pixels in size.
2) Right-click on each photo on your timeline and select Field Options, then check the option for Flicker Removal.
It can also help to prep your photos properly first in Photoshop Elements. Photos with very high contrast sometimes wiggle a bit in video. To avoid this, open each photo in Photo Elements and apply an Auto Smart Fix.
Welcome to the forum.
This ARTICLE will give you a bit more background on Scaling overly-large Still Images, prior to Import into PrE, and also how to batch Scale an entire folder, in either PS, or PSE.
Also, as Steve mentions, too high a contrast can cause flickering, as can over Sharpening.
Going back to the start of your Project, did you choose NTSC, or PAL DV for the Project's Preset? You should, if you are burning a DVD-Video.