Is this crown thinning or just naturally thinner hair at the crown? (photo)

This needs an in-person evaluation.  I recommend getting a formal evaluation with a hair loss expert. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

The crown is also known as the vertex scalp. Most people have 1 cowlick here that makes the hair swirl out from the center. Interestingly, a pediatric dermatologist once reported that right-handed people's cowlick tends to swirl clockwise and left-handed people's swirls counter-clockwise. Photo are fraught with flash effect and exposure issues that can make scalp pictures look better or worse that they really are. It's impossible to know if you have true thinning from these photos.  See a dermatologist to properly evaluate your hair.

Everyone loses hair all the time, maybe up to 100 strands a day. They fall out, then grow back in, and the cycle starts over again. But eventually, most guys will start to notice that they’re losing more than before -- and it’s not growing back.
As many as 85% of men will have some sort of hair loss in their lifetime. It can happen for different reasons.The gene may affect how sensitive your hair follicles are to a hormone called DHT, which makes them shrink. As they get smaller, the hair that grows back tends to be finer, thinner, and shorter. Eventually, it takes longer for hair to grow back. Then, the follicles will shrink so that no hair grows at all
The best option is seeing hair loss specialist to examine your crown area to know the reason of your problem a

Hello  sackings12, Its difficult to tell based on the picture.  
If you see hair on your pillow, in the sink or shower, then more than likely your hair is thinning.  We just don’t have any base line photo’s of the area prior to these pic’s to determine how much it has changed.
I recommend you to visit a hair loss expert to determine if you are indeed thinning and to help you find a solution for this problem.
Best of lucks!

The photos you submitted appear to show an early miniaturization/mild thinning in the crown region. It is important for you to understand that the majority of patients with male pattern hair loss will continue to thin as they age and that surgical intervention will do nothing to stop the hair loss process. Medical therapy such as Propecia and Rogaine can potentially help slow down/stabilize the hair loss process. I recommend a consultation with a hair specialist to further discuss hair loss and potential treatment options.