If you create an template-e-mail with Act! and add more than one picture they can´t be shown.
This problem is already known by Swiftpage when exactly the issue will be fixed isn´t exactly known.
An easy way to fix the issue is to set the pitcures into different data types.
For example the first one is a .jpgn and the other one is a .png.
If you are done with those steps, the pictures should be shown.