Not here to teach human anatomy here. but 2 things you have to keep in mind. Your veins do not always look the same when they 'pop up' above skin level, the temperature can change things, or different workout before photo session can push blood to different parts of the body, and veins look different. the second thing is, photographers retouch their images, especially rick day, you cannot possibly think all his photos just come out as 100% real! Photographers retouch photos to make them look good and hide models' identities.
not here to convince you or anything, so this is my last post on this issue. in the end, it's all in your mind, so believe whatever fantasy you have is the most important thing.