Hi Jeff,
Just found your post. While I recently started a newsletter, I don't use images yet, not sure if I will. With email getting harder and harder to get past the filters, I'd think images would compound the problem, I don't know.
Most of the couple dozen newsletters I do get are just text, however, I do get the free ones from Funds for Writers and each week Hope includes a different photo. I do know she uses Aweber.com for delivery now. Brian Judd (Special book sales) also uses an image in his too, not sure how he delivers it.
There are also a couple others that just send links and when you click, you go to their site where the full article along with images are held.
Hope that helps.