Thanks Graham but I need to include a prompt to allow the user to choose an image to do the replacement with. It was all so easy with that line previously with Word 2007, 2010, 2013 and some versions of 2016 but it seems to fall over on a few 2016 machines now and I can't work out why it doesn't work anymore. The Office2016FluentUserInterfaceControlIdentifiers downloaded from MS lists PictureChange as a command but apparently it doesn't work in all versions of Word 2016
The rest of the code works fine and crops the replacement image if the aspect ratio doesn't match the graphic it is replacing.