When I inserted images to Simple Pages, everything seems fine until I clicked save my edit then those images disappeared. I did try again with another empty page and insert one image but it happened the same. I can see the tag img in HTML editor but it’s gone when saving while the text works well. I’m using Omeka 2.6.1 and simple pages 3.1.1 .
Check the section HTML filtering in your Settings/Security. You can turn off the filtering there or just enable the desired tags and attributes (img and href).
I just added a plugin to the Omeka plugins that I have often used that will use an image from the images directory in your theme. It uses the img helper to load the file from that directory. It’s a shortcode plugin called Shortcode Anyfile. It can also use files from an item with or without a link back to the item or the file. In a Simple page you would just enter: