One can find three distinct images in Friar Lawrence's soliloquy in Act II, scene iii of Romeo and Juliet. First, in order to clarify, an image is
a word or phrase in a literary text that appeals directly to the reader's taste, touch, hearing, sight, or smell. An image is thus any vivid or picturesque phrase that evokes a particular sensation in the reader's mind.
An image in literature, therefore, can also be called imagery.
Onto the examples.
The grey-ey'd morn smiles on the frowning night,
Check'ring the Eastern clouds with streaks of light.
Here, the image of the morning light smiling at the escaping night is poignant. One can almost picture the sun smiling as it keeps getting brighter and brighter as the frowning moon disappears. The image which may come to mind may be very simplistic: a smiling sun and a frowning moon (similar to that of the typical child's drawing).
The earth, that is, nature's mother, is nature’s tomb.
The grave where she’s buried, that is also her womb,
And, from her womb, we find children of diverse kinds.
Here, the image is again very poignant. A reader could be imagining a grave where the silhouette of a pregnant belly is seen. From this belly, many different types of children can be born. ON the other hand, one could look at this image from a natural point of view. Meaning, with death in the world comes life (think plants being birthed from the belly (the ground) of Mother Nature (earth).
Two such opposed kings set up camp
In man, as well as in herbs, grace and rude will.
Here, the literal image and the figurative image can be pictured (much like the previous example). First, one can "see" two kings setting up their camps getting ready to battle. On the other hand, if using the previous quote as symbolic, the image one may come up with may look like plants taking up arms against both each other and man.