To determine the scale factor used to create the printed photo of the sandbox, we can compare the dimensions of the actual sandbox to the dimensions shown in the photo.
The actual side length of the hexagon in the sandbox is 40 inches, and the side length represented in the photo is 4 inches.
The scale factor can be calculated using the formula:
\[ \text{Scale Factor} = \frac{\text{Length in Photo}}{\text{Actual Length}} \]
Substituting in the values we have:
\[ \text{Scale Factor} = \frac{4 \text{ inches}}{40 \text{ inches}} = \frac{4}{40} = \frac{1}{10} = 0.1 \]
Thus, the scale factor used to create the printed photo of the sandbox is:
\[ \boxed{0.1} \]