Load an image to Photoshop or another editing program that works with layers

Save the image in PNG format

You will need that copy later.

Make an empty layer

Choose the Pencil tool and set it to size 2px and 100% hardness and black.

Choose the empty layer and draw your divisions

Make a white layer between the image layer and the drawing layer and save the drawing in PNG format.

The drawing has to be on a white background when loaded in ImageDivider

Open the ImageDivider program.

Load your image PNG in 'cmd1 - choose'

Load your drawing PNG in 'cmd2 - choose'

Click Run

ImageDivider splits the image after the drawing and

generate the average color inside each field.

Click Save

Open the result in an editor for further work.