IrfanView

When I have a hundred million images scattered on my computer and I need to quickly see them, nothing like a good script to herd them in a plain txt file and piping it to irfanview! No fidgeting with sixels, bat, or any other gui application. Hands down the fastest way… IMHO.

feh is very fast as well. But it is only a viewer and does not edit. But under Linux it is my go-to viewer, also for cases like the one you describe.