Measuring the exact height of an individual based on a photograph is nearly impossible but you can come close if the photograph offers a means of comparison. Criminal investigations often require an estimated height and they will use photographs to create a height range for a subject. For example, a frozen frame from a security camera in a parking lot might show the individual approaching a vehicle. The vehicle can act as a means of estimating the individual's height. It's not an exact science but you can measure height from a photo using a careful combination of observation and relativity.
Study the Photo
Before jumping into trying to estimate height from the photo, take some time and study the photo. Make a mark on every physical object in the photo. In an ideal scenario, you can locate other people in the photo that are standing shoulder to shoulder with your subject. Find their height and use common metrics to make an educated guess. The average height of a human head is 8.6-inches in the 50th percentile. If your subject stands a full head above or below another individual in the photo, you have a frame of reference to measure height from the photo. Make detailed notes and copies of the photo for markup if necessary. Write the height of each known object in the photo for a visual frame of reference.
Measure an Object in a Photo
Alternatively, look for static objects that have a known height. Vehicles are consistent across specific makes and models. Other commercially produced objects will have a known height as well. Objects like posts and structures are easily measured if you know the location of the photo. After measuring the actual height of each object in the photo, including your subject, use a ruler to measure the height of the same objects in the photo itself. Use a consistent metric like centimeters or inches for this process. Write each number next to the actual height size for your record.
Calculate the Height
Calculating the height based on the measurements is easy. Take your ruler measurement of an object and note the difference in height between the object and your subject. For example if your subject is two times the height of a car hood in the photo, you can apply that to your actual measurements by doubling the real measured height of the hood. This will deliver a fairly accurate estimation of the height of your subject. Use multiple objects in the photo to create a range of height estimates and take the average of the combined measurements for an even better assessment. For this to work, the individual must be positioned close to the object.