Tom McMillan's book is a god one. It is well researched. At page 152, it has the photo of the stock of the W Culp rifle. The credit for the photo is Gettysburg National Military Park. Based on that I think it is safe to believe that the photo is in their collection.
McMillan makes a strong case for Wesley Culp having been killed on July 2, and no one can say conclusively that his conclusion is wrong. However, my belief is that Culp was killed on July 3 because the regimental commander for the 2d VA, Col. John Q. A. Nadenbousch reported only 3 wounded on July 2, and makes no mention of any who were killed. (see OR, Vol XXVII, pt. 2, p. 521) With only one KIA in the regiment, it is hard to imagine that he got that wrong. Having said that, McMillan does present evidence supporting his conclusion. In the end, neither of us were there, so we really don't know.
Wesley Culp's body was never recovered, unless you believe the local legend that says the family recovered the body and interred it in an unmarked grave in Evergreen Cemetery. I have heard at least one person remark (only half kiddingly) that she planning to be buried in Evergreen Cemetery in order to be there on Resurrection Day to see if Welsey Culp is really buried there.