This particular field is designed to give more freedom to the users. In some cases this image field is necessary to insert signatures, drawings, schemes, sketches, architectural designs, etc...
By clicking on the Menu -> Create -> Image or by clicking the icon you can design and define on the form template:
width and height, by dragging the mouse to the size you want (it goes from 0 to 10).
To move or resize the Image field see: selecting, moving or resizing fields.
It can be positioned everywhere in the form and once placed, it can be moved or resized.
Options related to the image field:

Grid: In order to have a more precise drawing it is sometimes necessary to insert a grid that helps you geometrically define the correct position of the pen writing.
You can choose whether or not to include a grid. If you insert the grid it will be printed when printing.
Grid Size: With the grid size you can determine the space between the lines of the grid. The space value is measured in millimeters and goes from 2 to 10 mm.
Type of Image: In order to determine what type of image it will be you can click the Change icon and select the type you want. The predefined types of image that you can define are: signature, map, architectural design, equation, electronic schema, drawing, sketch or none (if you don’t know).