Adding photos to an eBook is quite simple simple. But it is important that they be photos that you have the rights to use.
As for making the book more interesting, this is true if the photos are relevant. Good style always makes it more interesting, providing it doesn't distract from the text or make it hard to read.
Many popular ebooks are just text. Others use graphics such as screen captures, photos, etc. to highlight what the book is about (especially how-to books) and still others just use them to add interest.
As for helping to sell it, I don't know if it makes a difference since people won't see the images until they've bought it in most cases. It may help with testimonials and word of mouth though.