Probably because I shot so much of it in film in what my granddaughters call the “olden days”, I just love a good black-and-white image.
Since I started digital, I’ve only once gone out with the intent of capturing images for b&w rendering. I usually find good candidates reviewing for that specific intent, sometimes years after shooting the picture. For what it’s worth, here’s what I’ve found:
Some subjects just beg the treatment:
I find steam locomotives to make great b&W subjects; most are already painted black! Steam makes for good tonal counterpoint. This subject category has one good general point, IMHO, that is rich blacks make a striking b&w image. Your zebra example illustrates it, too.
Interesting light sometimes translates into interesting b&w highlights:
Our kitchen counter gets great north light; this flower has some of it reflected off the left petal inward. This was a good color image, too. It helps there’s a dark background to highlight the subject.
My post-processing is simple: I usually increase contrast somewhat over what looks right in color, and I use the so-called BT.709 “luma” grayscale conversion, where each gray value = R*.72 + G*.21+B*.07. I use my own software, but I’m pretty sure GIMP has an equivalent option.
I sometimes “re-color” the grayscaled image with a blue-channel “linear” curve where the lowermost control point is just slid up the vertical axis about 5-10 (0-255 scale). This treatment makes the black tones look richer, in the manner of the old Ilford printing papers. You could probablyh get Agfa sepia by doing the same thing with the red channel, I think. Oh, when I grayscale my images, I keep them three-channel RGB just to do this sort of thing.
We used to shoot desert scenes with glorious cumulus clouds using a red filter; this made the blue sky just about black and the clouds prominent. I haven’t tried it yet, but I think you can do the equivalent in digital by changing the RGB proportions in the luma grayscale tool, e.g., R1.0+G0.0+B*0.0, or find the tool option that just selects one of the color channels to be the gray value. I don’t have a good cloud image with me to try it.