CARD DANCE/MOSAIC EFFECT

The trick is creating a layer large enough so that the individual tiles will be at their maximum size for your project. In the examples, the cards were never bigger than about 1/4 of the comp. If you are working in HD then each individual mosaic set to a size of 500 pixels would be good. If you want 50 tiles then the original image would be 50 X 500 or 25,000 pixels wide. You would build that in Photoshop and import it as a single file, not a comp. If your tiles are smaller then the image size can be smaller. If you want the tiles to move very quickly then the image can be even smaller. You will hide the pixels with motion blur.

The next step is to apply Card Dance to that layer. Card Dance is a seldom-used effect and the UI and workflow are not all that intuitive. You'll have to do some research if you are not familiar with how the effect works.  That's all there is to it.

There are some scripts of plugins that can generate a mosaic form a catalog of images and that will speed up the process a great deal.