From the full image ("The Beguiling of Merlin" by Edward Burne-Jones) one might select the following details, using the cropping tool from an image manipulation program:
 

Cropping tools vary in appearance. In some programs, simply clicking on the image and dragging a rectangle or square suffices to select a detail. More powerful programs display a variety of shapes and free-form selection tools:

In the example above, the cursor points to the tool for selecting a square; the option to the right permits a free-form selection. The tool below deletes all of the image not defined in the selection; use the Undo command immediately if you make a mistake (always keep an untouched copy of any image you manipulate.

The following illustrations demonstrate the use of the selection tool:

Beginning the selection	Completing the selection

 

Once the area is defined, most programs use an animated dotted line ("marching ants") to indicate a selection ready for copy or cropping. In the example below, the selected is copied (right click/copy) and then pasted into the discussion.
 
 

Detail selected

Further discussion.....
 
 

Although word-processing and web-page programs provide several options for the placement of images, e.g., at the beginning of a line of text as above, a centered image followed by discussion is the least distracting option for an analytical paper. "Flow-around" text is more appropriate for brochures.