Drawing Tool in WebForm
Image Editor will do that, 

Drupal 6 version allows to edit Imagefield items and save them back either by replacing the original image or adding new Imagefield item. but I'm not sure it will integrate with webform, You need to test it.

See the Demo Here


  Bring image editing (draw, text, crop, scale, etc.) functionality into
  your Drupal website! Edit/create any images online in the powerful and
  feature-rich image editors and save resulted images back to your site!