My code is at
http://jsfiddle.net/user1212/G86KE/4/
The problem is in gmail it leaves an extra white space between 2 tables inside the same cell. I have tried
Besides adding display:block to your img also add cellpadding="0" cellspacing="0" border="0" to your table (important: do not forget applying this to your wrapping table as well)
display:block
img
cellpadding="0" cellspacing="0" border="0"
table
Cheers