Gmail for iOS likes to automatically up the font-sizes and break your email layouts.

You can get it to also increase image sizes by using em for height and width units.

This is becasue 1em = 1 font-size so when the font-size goes up, the em size goes up too.

For example if you have an image that's 100px width and 20px height. Set
<img src=pic.jpg" width="100" height="20" style="font-size:10px;height:10em;width:2em">

Use it wisely