Specify the URL to the image you want to load. If you are using this locally, make sure to include the directory from this file (e.g. 'assets/myimage.png'. Then hit load.
Drag the points to fit the image. Then click save landmarks to save the points to a text file.
If you want to load a previous landmarks file, specify its URL (web) or file path (local), e.g.'assets/myfile.txt', and click load
If the lines are hard to see on your image, you can choose a color to change the line theme.