Custom coded email has blank Image when testing

I have set up a custom coded email, the same as many other times. This time, once set up, I sent myself a test. The image was completely blank, but anywhere there should have been a link, the link was there, and it worked. I tried testing to my iphone - the image showed up there and links all worked. I logged into my gmail account on the pc and sent a test to that email. The image was blank. Logged into webmail on my mac - image was blank. I sent the test to my boss, the image was blank for her as well.

Any suggestions or ideas on what is happening? Everything set up smoothly, preview looked great.