Just off the top of my head:
>
> #!/bin/bash
> for AA in DSC* ; do
> BB=`echo $AA | sed "s/DSC/Thanksgiving/"`
> mv $AA $BB
> done
If you have already Linux or some other Unix system, you can use mmv, which is part of many Linux distributions. It is available in Cygwin for Windows, too. So if you have Windows, first install Cygwin (it is a simple one-click installer, but choose the mmv program, when installing it), then open the shell:
cd /cygdrive/c/path/to/images mmv dsc\\*.jpg Thanksgiving\\#1.jpg
See "man mmv" for other features of this tool.