I studied under John Defazio at the SF Art Institute. He's known in the bay area ceramics scene as, I guess you could say, part of the Funk Ceramics movement (if you Google Funk Art you'll get the gist)... His work is elaborate frankensteining of slip casted disparate elements from kitsch and pop culture, often with intricate decaling, lustres, and many layers of underglaze and China paint. It's a bit like punk rock or underground comix combined with precious traditionalism in an ironic way. Strict "realism" or academic adherence to rules isn't really a focus but there's nods if necessary, if suits the work. I was attracted to the medium because of it's process oriented nature and it's marginalization as merely "craft" in the fine art world. Plus seeing DeFazio's work, and others like it, was simpatico with my own aesthetic leanings. I was a Glazer at Heath Ceramics, which is well known.

Anyway, painted "realistic" skin is probably difficult, texture painting with 3d painting tools is alot of fun. One of my favorite things really. Painting or working on other people's poser figures to the expectations of realism can be tiresome though. If I personally were going to try and create a photorealistic skin from photos I would get good high resolution full body reference from 3D.sk or similar and projection paint it onto the model. I have a similar resource I bought here for that purpose, made by BlackHearted, but I haven't really used it yet. Painting toon or creature skins is more open to creative interpretation.

Here's that resource...

https://www.renderosity.com/mod/bcs/sofia-high-res-human-photo-reference---extended-license/118225

You're probably are already aware of 3D.sk

Here's photo based projection painting in Mudbox... which seems a bit less tedious than the traditional method using seam guides and photoshop, though that still is very useful. There's a long tutorial on the latter method for Gen3 Daz figs by BT Sculptor IIRC, hard to find. Seems very difficult. Nothing but respect for the old school Poser skin creators for sure. A subscription to Mudbox is 10 bucks a month, sculpting tools are very good, 3d painting tools are fantastic.

https://youtu.be/gRZ5TUkmT-s