Obtaining the size of objects from an image

1. How do you calculate the size of an object in an image Python?
2. Is there an app that can measure from a picture?

How do you calculate the size of an object in an image Python?

to measure object you have to first find its contour. OR use Machine Learning or Deep Network to recognize object on image. You need to get the contours first, then fit a box around them, measure the dimensions of that box. That'll give you the size in pixels.

Is there an app that can measure from a picture?

With ImageMeter, you can annotate your photos with length measurements, angles, areas, and text notes. That is much easier and self-explaining than drawing only a sketch.