Slight shifting of image. The images seem to shift slightly from epoch to epoch. This is simply a measure of how accurately the telescope can be pointed. The pointing may vary by a fraction of a pixel, which causes a noticeable shift on the zoomed scale of these images. Most of the small roundish objects in the images are stars.
Variable stars are fairly common.
Some of the stars in the above images appear to vary. Some of the variable stars may in fact be Cepheids, but the data is not sufficient to discern the Cepheid characteristics. Another point to remember is that it is possible for a constant star to vary a bit in appearance in the sequence of blinked images, owing to slight differences in telescope pointing, exposure conditions, and the images processing used to create these images. Although space is a vacuum by Earth standards, there are still many high-energy particles called cosmic rays whizzing through the universe. Cosmic rays regularly strike astronomical detectors and leave streaks or blotches in the images.