I see a few people where having issues with centering or aligning their images side be side (horizontally)instead of vertically, and I have come up with a quick fix for this issue.
What you need to do is place the images inside a table and then center align the table where you see fit.
<table border="1" align="center">
REMEMBER - to put your 2 images in each cell. Add more columns or rows to suit your needs.
Have a look at my example: