The photographic paper inside of pin hole camera was scanned after the 6 month exposure and the post processing was done with Photoshop using curves.
Text added to help understand the image contents.

The objective of this ultra-long exposure was to show in a single image the variation of the path of the Sun and its altitude between the Summer Solstice and the Winter Solstice, resulting in 183 days - 4392 h - of exposure.
The image clearly shows the Sun at its highest point in the sky on June 21st, which corresponds to a greater number of hours of daylight, and progressively decreases its altitude until the lowest point in the sky on December 21st.
We can also observe dark areas in the months of July, August and September corresponding to clear and almost cloudless skies and from October onwards the increase in clouds meaning a lesser effect of the sun's rays on the photographic paper.