In technical photography, we use to photograph the object accompanied by something that we know the real dimension.

If you are shooting an X-ray, I recommend placing a ruler next to it, but within the frame of the camera.

Hope this helps!

Hi,

An interesting question. The first issue will be how the image is transferred to the phone. Is it just a hand held snap, or is it transferred digitally, wirelessly or otherwise? If it’s handheld, then all accuracy is gone, forget it.

The second piece of key information here will be the pixel resolution of the camera on the respective mobile phone. If you can obtain details of the pixel resolution (which would be pixels in width by pixels in height by pixels per inch/pixels per cm) then you can use this information to gain a reasonable idea of scale.

Simply measure the area on the image in pixels (there are numerous pieces of software with which to do this, such as Photoshop or even Preview on the Mac) and using the pixel dimensions of the selected area use the pixels per inch/pixels per cm figure of the phone’s resolution to work out a reasonably approximate size.

For example :if the area is 300 pixels by 75 pixels and my phone records at 150 pixels per cm, I know I am dealing with something approximately 2cm by .5cm.

From practical experience, I must emphasise that there will always be some inaccuracy, perhaps about as much as 1mm/50mm, so it’s not ideal for anything that requires pinpoint precision.

Hope this helps.

In technical photography, we use to photograph the object accompanied by something that we know the real dimension.

If you are shooting an X-ray, I recommend placing a ruler next to it, but within the frame of the camera.

Hope this helps!