Changing patterns e.g. water ripples. This can provide a pleasing pseudo-abstract pattern that varies each time you view the digital picture frame. If the image display time is e.g. 10 seconds, the sequence may not repeat for hours/days.
Another example is a pan of a tree trunk. This sequence works well on a portrait oriented display. It is also an example of the variety associated with a subject, i.e. one paper image may have been presented in the past, but via an electronic display, we can add many images that better capture the tree trunk variety.
Here is another example of a tree trunk. The version I use consists of some 2,400 images displayed with a delay of 5 seconds. The sequence takes about 3 hours to repeat. The change between images is only perceptible if you look very closely.
This is a close-up of some rusted iron. This works best as a slowly changing image sequence (10 seconds – 50 minutes to repeat). Using the electronic display allows 300 separate views of the iron detail in contrast to a single paper print image that misses the variety.