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:

IMG_0123.jpg
IMG_0124.jpg
IMG_0127.jpg
IMG_0128.jpg
...
IMG_0248.jpg
IMG_0250.jpg

could be renamed to this:

Camping Photos_001.jpg
Camping Photos_002.jpg
Camping Photos_003.jpg
Camping Photos_004.jpg
...
Camping Photos_112.jpg
Camping Photos_113.jpg

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).