How do we make hotspots trigger rollovers?

HI! How do we make a hotspot trigger a rollover. I have a circumstance that
needs this and I don't know how to go about this.
one image with two or more hotspots. when one hotspot is click then rollover
1.jpg will be triggered, but if the other is click then 2.jpg will be
triggered in the same location. Is this possible?

can someone help me?