In ES 1.2 the image popup has the close button on the left as seen here:
From a traditional stand point this is uncommon. We typically read from left to right (I know not everyone does). The user uses the right arrows to navigate through the pictures. Once they are done viewing they will have to move their mouse further to click the x button vs if it was on the right it isn't as far of a distance. However I'll comment that it is "more unique" having it on the left.
Here's a x button method that uses less space as seen here:
This post isn't to say which method is better, but more of a area of discussion and using the best practices for the close button placement.