When working with images, selecting a specific region of an image to work with is quite common. Therefore I made a script that allows you to generate a mask with one or more regions of interest (ROIs). The shape of the ROIs can be rectangular, elliptic, (irregular) polygon, or free-hand drawn.
You can find the scripts in my GitHub repository, which includes the classic image of Lena to use it in the demo. I suggest play with it in order to understand how it works. The scripts include plenty of comments in which I tried to explain each of the steps as clear as possible.
If you have any questions, comments, or feedback, please open a discussion. If there is a problem with the code (e.g., mistake), please open an issue. You can always drop me a line on Twitter (@amoncadatorres). Lastly, if you found this useful, fun, or just want to show your appreciation, you can always buy me a cookie. Cheers!