Hi,
I do not have a very valuable contribution to the discussion above, but inspired by the referenced wiki and reddit pages I tried getting the image previews to work and would like to share my experience:
I started with Uberzug. The code blocks referred to in the reddit post out-of-the-box 'worked' for me in the sense that images get displayed in the terminal. However, it all feels very buggy and non-robust:
1) In GNOME-terminal or Terminator when creating a second terminal tab the tabline appears and moves the effective VIFM curses interface area down. However, the image stays at the original location and then overlaps the terminal tab. Also, in Terminator with the image preview enabled and there being a horizontal terminal split with VIFM in the top terminal and another VIFM-unrelated terminal below, if one slides the separator of the terminal split to another location the image preview does not rescale to fit the VIFM preview area: the bottom terminal will be overlayed by the image preview when dragging the separator up.
2) When going to the VIFM subshell by pressing the 's' key the preview image stays visible overlaying the VIFM subshell interface.
This behavior is identical for GNOME-terminal and for Terminator. It seems like the Uberzug image is bound to the parent terminal emulator (and its dimensions) rather than the VIFM curses area.
The w3mimgdisplay method explained in the wiki.vifm on the other hand works perfectly without any of the issues mentioned above, although it did force me to migrate to XTerm (with tmux for multiplexing) since w3mimgdisplay does not work in GNOME-terminal and Terminator (for me on ubuntu 18.04). Moreover, in the process one gets a terminal text-based web browser for free -w3m- ;)
I post this message here for documentation purpose hoping that someone understands the Uberzug behavior and knows how to 'fix' (i.e. improve) it. As far as myself is concerned I may just stick with w3mimgdisplay+XTerm+tmux anyway ...
Kind regards,
A very happy vifm user :D