Start HDevelop or, if it is still running, click File ▹ New Program to start a new program. HDevelop will notify you if there are unsaved changes in the current program. If it does, click Discard to throw away the changes and start anew.
The first thing to do is read the image and store it in an iconic variable. From chapter “Acquiring Images With HDevelop” we already know that we can simply drag an image to the HDevelop window. We also know that this inserts the operator read_image into the program. Therefore, we can just as well insert the operator directly.