I'll give you a few examples of imagery in the play. I'm afraid that the play is just too rich, and there just isn't enough room here to list them all.
I.1: ...her sunny locks
Hang on her temples like a golden fleece;
Which makes her seat of Belmont Colchos' strond,
And many Jasons come in quest of her.
Bassanio is bringing to mind the image of the golden fleece in his description of Portia's hair. This is also an example of an allusion.
II.1: Besides, the lottery of my destiny
Bars me the right of voluntary choosing;
This speech calls to mind the image of the lottery to decide our fates.
III.2: The painter plays the spider, and hath woven
A golden mesh t' entrap the hearts of men
Faster than gnats in cobwebs:
III.3: Thou call'dst me dog before thou hadst a cause,
But, since I am a dog, beware my fangs;
IV.1: I am a tainted wether of the flock,
Meetest for death; the weakest kind of fruit
Drops earliest to the ground, and so let me.
IV.1: The quality of mercy is not strain'd;
It droppeth as the gentle rain from heaven
Upon the place beneath. It is twice blest:
It blesseth him that gives and him that takes.
The concept of mercy is given substance in the image of rain that falls gently from the skies.
V.1: That light we see is burning in my hall.
How far that little candle throws his beams!
So shines a good deed in a naughty world.
I hope this helps!