^ Thin black borders work to define the edge/extent of a pic when the background of pic surround is similar.
Jay's shot is a good example.
Otherwise, I think it best to judge each picture whether it benefits from a border or not and and how thick it is. I don't think it's a good idea to establish a blanket rule of having a border on every pic you take.
I use Adobe InDesign and can alter the weight and colour of any border but that's a fairly major app just for that. InDesign delivers all sorts of customisable border effects but is a graphic design app:
^ By pure coincidence those 2 pics go together quite well - It's JC's "naked" quote which does it!