If you want to insert images or photos to your e-book, you'll have to make sure they're yours or that you have the right to use them. Buy ideal ones on stock photo websites and agencies. You don't want to have problems with this later on. Photographers often experience copyright infringements, because people take their work for granted. People see thousands of images online and they come to believe all of them fell from the sky, or something. It's a big thanks to photographers and graphic designers, who put their time, energy and eventually money to make those photos happen.

You can find plenty of photos appropriate to almost any niche in the world on photo stock websites. Just google 'photo stock', or 'cheap photo stock', if you're financially limited. You'll find all sorts of photos and images you'll be able to use for less than a few bucks.

Another way of doing this is to create your own photos. Take a camera or a smartphone, which probably has a decent camera on it, and find whatever you need on photo in the nature. Take a few shots, then transfer it to your computer. Sometimes you wont' need any graphic editing, but sometimes you'll need to use a photo editing software like 'Photoshop'.

Images should be of great quality and look really nice to make the reader want to look more in the ebook and read more. Overall graphic design and font should be in the same manner, also.
Don't skip this part. Make everything as beautiful as you can.