A technique for inserting form fields into forms displays a cursor superimposed over a background image of a form and dynamically generates candidate shapes of a form field to be inserted. New candidate shapes are generated automatically, based on pixel content of the form under a cursor, as a user moves the cursor over different regions of the form. In response to the user manually selecting one of the candidate shapes, the technique establishes the position, size, and shape of the form field based on the position, size, and shape of the selected candidate shape. The improved technique thus proceeds semi-automatically, generating candidate shapes automatically but based on manual, user-directed cursor positioning and manual selections.