This change occurred over the week-end and could have a massive impact on the way your creative will display in Gmail.
Funny thing is this only impacts sliced images (read here a big image cut into smaller ones) since what Gmail does is that it adds a slight space around the image.
The solution spotted by the guys at Smith-Harmon is to add (in-line of course since Gmail doesn't read CSS) the following parameter to your image tags: style="display:block"
Here's an example of correct image tag:
< src="”http://www.example.com/client/images/logo.gif”" alt="”CLIENT”" border="”0″" height="”75″" width="”200″" style="”display:block”">
Once again, the only real impact of this change is on sliced images, but you're always better safe than sorry.