Have you tried putting these inline codes on TD of the images: font-size: 0px; mso-line-height-rule: exactly; line-height: 0px;
When I removed my font styling from the <td> the horizontal line disappeared.
After some investigation I fixed the issue by changing my line-height. It was originally 15px so changed to 1 (no px). Also 14.9px worked too. interestingly any larger px value retained the horizontal glitch.