Create JPEG Images from PNG's on your Mac Desktop

I like to use the PNG format for Mac screen-captures to ensure that I don’t lose any clarity in the source images. I often convert these images to JPEG format for inclusion in email or posts. I got tired of running the conversions by hand. tojpeg.rb is a Ruby script for OS/X and MacOS that uses the sips utility to convert the PNG files in ~/Desktop to JPEG counterparts. The PNG files are left intact.