Which one is an unaltered photo of my favorite mug and which one is rendered in Cycles + PS? Look carefully. This one might be too easy.
Click for higher resolution
The left one is fake
I think that the right one is real mainly because of the dusty worn seam where the handle meets the mug seems to add to the realism. But the stain on the left cup looks more real, hmmm…
Hey Photox
You doing a really good job with this and making people look more than once, for me the left is fake, the shadows do not look correct.
Shaun
The one on right seems like having reflections more “real”: more details and color in the highlights, irregular surface, unless you overdone them on purpose 
What light setup you used?
Then you written " unaltered photo" : a trick is to check at the histogram. The photo have a “uniform curve”, while with the other seems like you did some postprocessing that created some cut and spikes in the high value pixels.
left - digital photo, right - virtual image… 
edge modeling, beveling gives you away too
Left. shadows
Current votes:
Left is fake 4
Right is fake 1
In the spirit of the challenge I’d encourage anyone to pick their answer and post before looking at the answer. It is also possible, as mik points out, to spot the post work by missing spikes in the levels histogram. Anyways, here is the answer – and a surprise cameo by Gary Busey!
My vote on this one is left photo, right render. If the left one is the render your skills are better than reality, right now But the remains of coffee with the condensing one of the drops has at the bottom, the subtlety of the material and the shadows let me think of the left one as a photo.
Kudos for the right one also, if that’s the render. Presented alone that could easily pass as a photo.
i say left fake
I say right is fake, for the same reason I said that red lighter is fake. The reflection fresnel and intensity is too much for that kind of material. But this time it was harder to decide 
Good job !
To me it was ground decisive - to much reflections for such a cracks.
Good job with these riddles, anyhow.
But this time the histogram didn’t work well:
I thought the spikes in red and the less overall value range were becouse of Photoshop? Or it’s simply the downscaling?
Hmm, that is weird. I did downscale it. But that was the only thing. For posterity I’ll post a link to what comes out of my Nikon COOLPIX L820, a jpeg. It was copied and pasted on my drive, cropped, and scaled down.
I wonder if it could be jpeg compression (when I saved my PSD file for BA) I’ve had issues posting .pngs here so I just go for jpegs. When I started making my final round of tweaks on the mug, I went over the comments on the BIC lighter and made changes that weren’t necessarily in the direction I saw in the mug in front of me, but seemed to be swaying people. It was fun to model, I held the mug in my left hand and modeled with my right.
It seems that the pros here have rightly called me out, but certainly in the beginning a lot of people were convinced that the photo wasn’t real.
IMHO, checking curves is the last resort. Though if done right even that can not suffice to recognize a “fake”.
I noticed in your previous image (lighter) that you like to model anomalies though you are inconsistent with real details (thickness of metal part, too much cogs on a spark wheel…).
Here was obvious that the handle you modeled is slightly thicker in upper middle part (inconsistent in thickness) & the cup’s top edge is too narrow, thin…
Also reflections, stains, shading, DOF, noise, lens aberrations… are another give away. (Haven’t found the magic solution yet, though PRMan & C4D physical are getting quite close).
Thanks & Keep up the good work.
Left is fake, it is too perfect. But so realistic!
liquid helix, high praise, and it certainly is! :rolleyes:
Burning, thanks, great feedback for future projects, you nailed all the usual suspects of cheap tricks to use in the valley. Guilty on all counts.
Is it cheating to intentionally make the photo look CG? I figure the goal of these is to either make the images as similar as possible, or otherwise use two completely different images as a more general test. Left is real, right is fake.
Zeke, it’s a valid point, no doubt. I would say it’s cheap, but not cheating. I took the photo on my bathroom counter with the regular items nearby. That said I was hoping for a photo with less reflections and more even levels. It was somewhat cheap and I won’t dodge it. I’m going to buy a tripod and read up on how to get the best from my camera. I’ll take a few weeks and get a photo of something relatively complex in its natural environment, and attempt to match it. My new plan is to use much higher res procedural and uv grunge (no “real” photo textures, like the granite), render at a higher res and then scale it down. With better planning and more time I’m confident in my chops to have even the eagle eyes in the community scratching their heads. You’re a straight shooter, I respect that.
Either way, great job