Some cases are unique – and this will describe one of those. In this case plaintiff retained me to determine if a photograph of a part was broken. The part was a water jet from a bathtub spa. The person using the spa was injured, and the reason proffered was that one of the legs that hold the jet in place was broken. The hotel personnel recovered the broken jet, placed it on a table and took one photograph of it. Later, the jet was lost before any expert could analyze it.

I was retained to determine if the leg of the water jet in the photograph was broken. The jet had three legs and the one that was believed to be broken was the one on the back side when looking at the photograph. Looking at the photograph, that leg appeared to be at a slightly different angle, but defense claimed that the leg was not broken and that the slight difference in angle may have been from the angle of the photograph, the lighting, the focal length of the camera lens, or simply the way that the jet was positioned on the table – or perhaps it wasn’t at a slightly different angle at all.

Measuring the angles of the legs to the front of the jet wasn’t possible because we had only one image and the leg in question was on the back side of the jet. A 3-D model couldn’t be built because there was only one photograph. But, a reverse projection analysis could be done. Reverse projection involves taking a new photograph from the exact same position as the original image, then one can have the data needed to make comparisons, make measurements, compare lighting, etc.

In this case, plaintiff provided me with a new, unbroken, water jet of the same make and model as in the original photograph. I placed it on a table in the exact same position as in the original. I set up lights to exactly replicate the lighting in the original, with all highlights and shadows matching. I set my camera into the same position that was used in the original photograph, and I took the picture. Next, I created an overlay of the two photographs. The result was conclusive – everything on the two water jets matched except for the one leg. The leg had to be broken on the jet in the original photograph, as there was no other explanation for the difference in the two photographs. The difference between the angle of the leg in the original photograph and in the new photograph were measured, and made part of the illustration.