Just an observation: partly this frustration is caused by how Anki (or most spaced repetition tools) works by default. That is, the difficult images come up most often. This easily creates an illusion of never learn to remember these. So since in reality most of the image recalls range from easy to somewhat challenging, I guess I should focus on improving those more difficult images instead of falling into that illusion of defeat.
Still, even if this system never becomes as fast and as practical as my PAO, there's definitely a fun challenge in it, and the idea that any three-digit number out there has an image relating to it in my head. And maybe some day (I still got years, maybe even decades ahead of me) they become so ingrained that the recall process becomes automatic any time I see such a number sequence.