It depends on the book and the effect you are trying to create. It also depends on the intended reader and the images itself. Not all readers have the same size and resolution. Also the font size plays a big role, especially when you want to flow the text around the images.
For example, in the retail epubs of Narnia illustrated by Pauline Baynes the images are between the text. However, sometimes you can see that the text was mend to flow around it. When the images are big, a separate page would be better.
Keep in mind, that because of the flowing character, if you want a separate page for each image you could end up with a few lines on a page and the rest of the page blank, than image and then the rest.
There is no real common practice, at least not for me.