Please ensure that your picture files are named sequentially as 1, 2, 3 4 etc and they carry either jpg, jpeg, or png extension. For example, the file names should be 1.jpg, 2.jpg, 3.jpg, 4.jpg etc.

It is always better to use Cycles engine for the perfect outlook. If you are using Eevee, you can consider a higher value for the emission strength field in this add-on. It will produce a better color and a better appearance for the pages, but the shadows may be impacted. So you need to do a trade-off for the best result, or switch over to Cycles.

If you are using a backside picture, you should keep the page thickness as zero, otherwise the backside won't take effect. This is a limitation as of now. If we get user requests to improve on this, we will remove this limitation.