I noticed that every time you apply certain filters to an image they run differently each time. I thought it might be fun to check out the image stacking in Photoshop's new 'extended' versions.
I chose coarse settings for the pixelate > crystallize filter - course enough to disguise the photo. Below is a stack of 8 such images averaged together. The more you use, the less the filter disguises the original.
Here is a (tedious) method for stacking images without the extended version of Photoshop
I was playing around with this. For image averaging you don't actually need Photoshop Extended. You can do it in any version of Photoshop that supports 32-bits:
Stack the images in layers. Use the LINEAR DODGE (ADD) blend mode to sum all the layers. You will blow out the image way past white. No worries. Kick into 32-bit mode and dim the sum (no pun intended :D ) back into a usable range. For a true average, dim it by a factor of (1 / N layers)