Hello Vanda thanks so uch for your answer. You really shoud work on it. As you may see it’s not nice that all the prezis of everybody loo the same all ovber the world : a dark grey square. Prezi is a visual tool so it shoul look nice in the sites where the presentations are embebed. it´s not good for the image of your product to have such a negative point. I like Prezi very much but there are some detaisl that can ruin a good tool and this is one of them. Even if you don’t want to give us the chance to edit or choose the thumbnail, you should at list put something else by default. For instance for the free acounts it would be the firt slide of the presentation. And for the people who pay the possibility to change the thumbanail.
Its a advise of someone who likes PREZI.
Hope you solve this matter soon
Best regards from our team of the Lisbon School of Agriculture