[mrmikel]

If you are trying to change the size of images already inserted you can right click to open with and edit them with any image editor already on your computer.

If you want a program that will allow you to resize images "on the fly," Atlantis Word Processor does this in addition to allowing to you to paste images into the document you want to be an epub.

The pasting process works fine, but it lead to some bloat if you reuse an image repeatedly, as it stores the same image every time you paste it in.

AWP, however, only publishes your epub after you are done editing. It does not edit the epub itself, so if you wanted to make changes you would go back to the original rtf, work with it and publish it again.