I saw a book in a used bookstore around 2005 in Ontario, Canada whose cover art really caught my eye. Unfortunately, I didn't end up picking it up, and it's been bugging me ever since.
While I saw it around 2005 or so, it seemed to be far older; it seemed more like a '60s or '70s pulp paperback, and was relatively thin, I'd say about 200-300 pages.
The cover art itself was somewhat minimalist; it was plain white, with a monochromatic, almost wood-cut-style image on it in brown or black (similar to this). It almost seems to me like it may have originally been interior art from a magazine like Astounding, Galaxy, etc, adapted into cover art. I also seem to recall the paper for the cover itself was very fibrous and low-gloss, almost like canvas or Bristol board.
The image itself was of a steampunk-looking humanoid robot or soldier in power armour, with the suggestion of a warzone in the background. The figure was in mid-stride past, while looking directly toward the perspective of the cover. The figure itself was fairly thin - it's possible at least the limbs were mechanical "pipes" and wires - and the head consisted of a slightly tall and pointed helmet (reminiscent of a British pith helmet) with round-lensed goggles. A good reference of both pose and general look can be seen here.
I could be wrong, but I seem to recall the title had the word "Armor" (or "Armour") in it, though searching both on IMDB returned nothing similar - it's not Armored, Body Armor 2000, or Armor. It's possible it was an anthology of stories involving power armor or war robots, but I couldn't say for sure.
