For an example of death imagery, take a look at Act IV, Scene I, when the three witches are casting a spell. They list "finger of birth-strangled babe" as an ingredient in their potion. This image of a dead child emphasizes the dark and sinister nature of the witches' magic. It is also important in creating a dark, disturbing mood as the three women cast their spell.
Next, for an image of darkness, take a look at Act I, Scene IV, when Macbeth hears that Malcolm has been named as Duncan's heir. For Macbeth, this creates an obstacle on his path to becoming king, prompting him to create an image of the stars extinguishing their own brightness:
Stars, hide your fires;
Let not light see my black and deep desires.
Finally, for disease imagery, turn to Act V, Scene III, when Macbeth is talking with the doctor. In this image, Macbeth also personifies Scotland as a diseased person who is in need of a cure. Moreover, he compares the English to a disease which needs immediate treatment:
If thou couldst, doctor, cast
The water of my land, find her disease,
And purge it to a sound and pristine health...
What rhubarb, senna, or what purgative drug,
Would scour these English hence?