Using Views "Rewrite the output of this field" tokens
There's a simple way to show only the first image in a field that allows multiple image uploads. 

In the Configuration screen for the field, there's a dropdown called "Multiple Field Settings." Expand that, and you should see options for how many items you want to display, and which item in the list to start with. Change "Display __ value(s)" from all to 1. You shouldn't need to change the separator in your case, as you're only displaying one image. 

See below for screenshot. This setting should work fine alongside "Rewrite the output of this field" tokens (I haven't had it not work).

http://img585.imageshack.us/img585/8644/multipleimagesshowonlyo.png 

In a field with several images uploaded, I'm correctly seeing only the first as you can see here: 

http://img713.imageshack.us/img713/5479/resultzc.png