Note: Before attempting the following make sure you have a backup copy of all the images before performing any bulk renaming functions. Red Rook, Inc is not responsible for the use of 3rd party software.
Image file names in Magento are case sensitive. Therefore an image name: Picture.JPG is different than Picture.jpg
It is HIGHLY recommend that all product images that get uploaded to Magento use the same image type and case.
The following 3rd party tool is an easy way to bulk rename image filenames
Download the Bulk Renaming Utility from the following Website
The settings below will allow you to Bulk Rename item images to be uppercase and the image name extension to be lowercase.
How to Bulk Rename from a Command Line
Download "Bulk Rename Command"
Example - The following will replace the extension .JPG with the lowercase .jpg
"C:\FILEPATH\BRC64.exe" /IGNOREFILEX /REPLACECS:.JPG:.jpg /EXECUTE