Synx already pointed out a lot of stuff. So I try not to repeat too much.
First things first, there are different kinds of realism. Most people are thinking about
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or even
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, so I assume, that this is the case here too.
When you want to achieve a photorealistic image, then there are four building blocks, that need to be used properly to avoid the uncanny valley, and your bad luck is, that living beings in general and humans, in particular, are the hardest things to render photorealistic from a human perspective.
The four Building blocks are.
1.) The Model: You need a high-quality, model with realistic proportions in the first place. And those correct proportions have to be on every level of detail, starter by the silhouette down to the golden ratio of the face. A cartoony figure can only result in a cartoony image. The human face is the one thing next to genitals, that the human mind processes as fast as nothing else. No thinking involved, just pure instinct decides if we think that the thing in front of us is a digital puppet or a real human on a photograph. So bad gestures and body poses can somewhat be compensated, a bad facial expression can't.
2.) The Materials/Textures and surfaces: Good looking materials have to behave properly. A metal never has a coloured reflection, a water surface is never flat etc. (The key here are normal maps, colours, different layers on surfaces, displacement and imperfections.)
3.) The Light: A realistic image needs a realistic lighting setup. You can have Disney MCU level of hard- and software when you place the sun below the heroes while they stand on the ground, you will just get an ugly image. Light has certain attributes that need to take into consideration. Soft vs. hard light, the colour temperature of light sources, fall off. Just to name a few.
4.) Camera behaviour and postprocessing: Last and considered by some schools of thought also the least. I think it is as important as the other three. You said you worked your images in PS. Why? Also, what kind of camera did you want to recreate? The term photo isn't in photorealism for nothing. There are lense distortions, lens flares, chromatic operations etc. Those effects are often built-in within the postwork process. Some effects can be done while rendering, depending on the render engine. As a rule of thumb, you can say, every effect a photographer want to remove from his/her picture, a CGI photorealist wants to build into the image. Renders a crisp sharp all over the place, a real photograph has the depth of field. A CGI cam stays perfectly still, a photo camera doesn't, even with a tripod.
