Maybe it's late and my mind might be fried for the day, BUT I did not like Bookr. I can see the advantages to using a tool like this to allow kids to make a creative product for any classwork, projects or research they do. In the short visit to Bookr, I did not find a lot of flexibility or creativity. Again, it's late so I will be sure to visit the site again tomorrow and give it a second chance.
I found a similar website that is VERY user friendly, and provides a large variety of creative templates, images, and tools. I used Mixbook and was able to create a photo book. http://www.mixbook.com/photo-books/all/vintage-wedding-copy-4560382 which can be viewed here. Students could either do a google search of images they would like or they could participate in a project where they journal a lab or their work with digital cameras then insert their images on a mixbook album/book. In searching their public gallery, there are many samples of books under the education tab.
Here is one created on the water cycle for 5th graders.
Here is one created to explain the concept of acids and bases.
These books can be ordered for print which could make fun gifts to a school library or to parents and teachers.