To annotate an image, you must be logged in with Author privileges for the Scalar book containing the image. Navigate to the image in Scalar, and click the "Edit annotations" button at the bottom of the page. This will launch the annotation editor. Once in the editor:

1. Click and drag your cursor across the image, drawing a rectangle around the area you wish to annotate (once you've created the annotation, you can adjust or fine-tune its area and coordinates by modifying the values in the X, Y, Width and Height fields in the annotation editor).
2. Enter the title of the annotation in the field just below the rectangle.
   
3. Click "Save."
4. Alternatively, instead of drawing out a rectangle, you can click the + sign at the bottom of the annotation editor and manually enter the coordinates and width and height for the annotation. 
   
5. Enter the content of the annotation (optional).
6. Enter an abstract for the annotation (optional).
   
7. Click "Save" at the bottom of the annotation editor.
   

Additionally, you can click any annotation in the annotation list on the left to select it. Selected annotations can be edited using the provided form, or deleted by clicking the minus button. When you're done editing annotations for the file, click "Done" to return to the page for the media file.