Is there a way to determine if photographs of horses/riders have be photo shopped?

It can be done just using your eyes if you know what to look for--but there sits the skill of the photo-shopper. Some people are amazingly good, and you'll have the worst time telling if something was photo-shopped, on the other hand, some are unminstakably photoshopped.

Look for things like:

changes in lighting through out the picture (shadows, amount of light on skin/face/objects, etc.)

color/contrast (darkness, shades of things...sim to lighting)

seams (obvious seams sitting in the picture)

edges/cut areas (similar to seams; things you think may be from another photo, but that were cut out and put it, or oppositely, things that were there, but were taken out)

natural effects (dust, splashes, shadow, footprints, texture, etc.)

pixels (if you zoom in close enough, you might be able to tell the differnce in pixel quality/count in different areas of the photo at the same zoom length. if area 1 of photoA is very pixely @ 200% zoom, and area 2 of photoA is barely pixely @ 200% zoom---it was photoshopped).

It depends more on the skill of the photographer or graphic artist doing the photoshop work. I personally do not change anything that would turn a conformation photo into a lie. I will replace an eye if it is closed, but try to use the same eye on the same horse in another image that is close to the same size and pose as the problem photo. I can fix an eye so you cannot tell unless you look very close. I don't fix ears, but that is a place you would look for cloning artifacts. I fix eyes when I use a on camera flash. That is the easiest photoshop fix to see, but honestly the fix looks better than the bright eye. I also fix studs that have dropped and that is another place you can look for cloning artifacts. I work principally with cutting horses and have been known to move cows to a closer position. That is tricky because the eyes of the rider and horse will give away the true position of the cow. I do remove trash from the background such as water bottles on the fence, cowboys on the cattle pens, etc. Note: Most photographers will not spend much time changing images with photoshop unless they are paid well. They might charge $25 to fix an ear or eye, but they are really going to charge if you want them to change the topline, and many won't do it on ethical grounds. What are you looking to discover in finding these photoshop fixes? DId someone supply you with the photo of a horse you want to buy? If so ask for several photos to compare.

If you can load the image back into Photoshop and zoom it you can usually tell because even the most careful graphics artist cannot match the rasterizing and blending capabilities of the program.

If It's an image in a magazine etc then it's likely that it will have been manipulated in some way.

Can you maybe add a link to the image so we can get a look at it for ourselves ?

What is the source of the photograph? If it's in a magazine of some kind, you can write or email the editor and ask them what their policy is on accepting photographs. I remember some years back (in the days before Photoshop and other programs made it easier to tinker with pictures), one of the Arabian breed magazines took a lot of heat for publishing ads that had photos that were either touched up or reversed. If I remember correctly, they changed their policy on ads and wouldn't accept anything that had been retouched or reversed.

This depends entirely on the skill of the editor. In some instances it may be almost undetectable by any means other than specialized software. Usually however, for the average photoshop user, discrepancies are detectable, particularly if you enlarge the image.

Do you have any examples you'd like us to check?

There is software you can use to detect layering of pixels, which is what Photoshop uses to combine images into one.