Depending on your project, not all files which are under version
control are text files. Most likely you will have images too, for
example screenshots and diagrams for the documentation/helpfile.
For those files it's not possible to use a common file diff tool,
because they only work with text files and diff line-by-line.
Here is where the Tortoise Image Diff tool (TortoiseIDiff) comes
to the rescue. It can show two images side-by-side, or even
show the images over each other alpha blended.