I am pretty sure I'm prosopagnosic. It's a mild form - I can actually recognize people by their faces, if I know them well, they look weird, or I've concentrated on trying to learn their face. But I can't recognize people as easily as most people do. For example, I had a counselor for several months, and never learnt to recognize her face - I recognized her as 'the person who comes up to me in the waiting room and leads me into her office. She was young, and I think she had long blond hair, but that's all I remember.
I'm not sure if being autistic makes it easier or harder to cope with prosopagnosia. On the one hand, autism interferes with a lot of the work-arounds for prosopagnosia. I can't keep track of a lot of personal details about different people, so if someone mentions their husband Bill that usually isn't much help. I don't know how to get people to say something that gives away someone's identity, without revealing that I haven't recognized them. I also don't pay much attention to how people look, so hairstyle, accessories, clothing are not as much of a help for me as for non-autistic prosopagnosics.
But I have absolutely no interest in gossip, so when chatting with people I talk instead about ideas, and the person's identity is not as important for that. I don't make friends easily, and don't mind being alone, so I don't need to keep track of as many people. In crowds, I'm usually not looking at other people, so my lack of recognition of someone could be attributed to not having seen them. I'm more often in the company of my parents, because I have trouble with things like traveling alone by bus, so my parents can help me remember who a person is.
And more importantly, I don't seem totally normal like many prosopagnosics do. I can pass for normal, to a certain extent, but anyone who knows me more than superficially knows that I'm pretty weird. And I'm one of those 'extremely out' autistics who tends to tell everyone I have a decent-length conversation with about my diagnosis. The fact that I fail to recognize people on occasion, therefore, gets seen in the same light as not knowing what time of day it is, not realizing two people I know very well are in a relationship together, or not understanding a bit of slang. The fact that I have so many more quirks than a simple prosopagnosic means that people are less likely to forget that I'm different or not believe me when I tell them I have a disability.
In that sense, then, it's easier to deal with prosopagnosia if you're autistic. Although high functioning autism is called an 'invisible disability', it's more visible than prosopagnosia is, which means people are more likely to understand and set aside normal expectations.