This is a great idea; thank you very much mediaguru.
For anyone else attempting this there is just one problem, I initially tried deleting / replacing the nophoto.jpg and the tnnophoto.jpg in the following directory:
com_comprofiler/plugin/language/default_language/images/
but I was blocked. I have tried FTP and Cpanel and within each there was something stoping me deleting or renaming the files.
In FTP I get a critical transfer error'
In Cpanel I get 'Permission denied'
I eventually done it by deleting the jpg files using JoomlaExplorer and then uploading the new image (with the same file name), again using JoomlaExplorer.
Thanks and best wishes,
Gary