When vectorizing an image, you can either vectorize the entire image or just a portion of it. 

Load the desired image on the editor, either by Taking a Picture, Loading an Image File, or Loading a Server Image. 

The image is loaded into the Trace editor.

Enter the desired size for the image in the Design Bounds section. 

The image will resize.

Draw a box around the section you wish to vectorize.

Click the Vectorize button. 

The selection bounding rectangle of the image will be vectorized.

Have the image with the selection bounding rectangle on the screen.

Click the Clear Partial Image Bounds button.

The selection bounding rectangle is removed.

You can either select a different portion to vectorize or vectorize the entire image.