Batch JPEG Photo Renamer

I used this script all the time before Picasa finally added this functionality. This script renames a whole bunch of photos, in a directory for example, appending numbers to the end of a base filename according to the EXIF dates stored inside the JPEGs. For example, a directory full of files that looks like this:

could be renamed to this:

with Camping Photos_001.jpg being the oldest photo in the bunch and Camping Photos_113.jpg being the newest, according to the EXIF data. The separator, base name, and starting index are configurable. And if for some reason EXIF is missing from the photos, you can choose to use the current ordering (ie. IMG_0127 was taken before IMG_0128).