Look in /usr/share/applications for your .desktop files. Open a few of them and look them over to get an idea of how they are constructed.
That's what I was trying to do, but I was confused as the .desktop extension does not appear on screen in the lists in PCmanFm as I have it set up. All I get is an icon and the basic application name. (Nor could I locate
any files in that folder with a .desktop extension.) However, I find that they are listed as desktop configuration files under the detailed view, so I opened one with leafpad and can more or less see how they work. The obvious thing is to edit a copy of the xsane file. And I'll need to create an icon, which I think I can do.
However, there is a problem, the .desktop files assume that the program is properly registered somewhere and can be called up from the CLI by typing its name - this doesn't work with vuescan as all I did was to pour out the contents of the .tgz file into its folder in /usr/share/. I can enter "xsane" and up it comes, but "vuescan" gets the "command not found" response.
I'd be interested to know how I can do this.