According to Zumwalde and colleagues, a growing trend on the internet involves the reports of strange handprints on mirrors and windows. These hand prints have been attributed to some as ghostly or alien handprints? These researchers decided to examine how and why such prints might be occurring.
Zumwald first attempted to recreate the handprints by using a variety of cleaning products and then washing them off. The goal of this was to determine if a residual handprint could occur naturally from a person placing their hand on a window or mirror while cleaning. Their tests failed to produce handprints when steam was applied to the window panes. Cleaning gloves were also effectively ruled out as the cause of the hand prints.
However, results from digital photography demonstrated that simple hand prints can be distorted to create the handprints. In the case of handprints inside a double pane of glass (and thus untouchable), the researchers were able to determine that humidity makes silver particles between the panes cluster on the handprint, thus creating the effect.
Long story short, no ghost or alien is necessary for this particular phenomena.
Submitted by: Brian Laythe
Reference. Zumwald, A., Ciriaco, K., & Allison, J. (2016). Strange handprints in strange places. Journal of Scientific Exploration, 509-523.