If you want to open the file in the default application then that was already answered. If you want to do the same the Explorer is doing on "Edit" context menu item, then add these two lines in "Original, complicated answer" from the link above:
if (psi.Verbs.Contains("Edit", StringComparer.OrdinalIgnoreCase))
psi.Verb = "edit";
You should check the existence of the verb you want in psi.Verbs
as per the MSDN. If there's no "edit" verb then the code calls default app.. by default.
If you want to give the user a list of all image editing apps that the user have installed then you would have to have a hardcoded database of such apps together with their installation GUIDs, check if they are installed, find out where they are installed (maybe not in the default place), and make a list of them, calling each with your file as a command line argument. It's too complicated to give code for that.