In the Temple, there was a thick curtain, behind which only the High Priest could enter once a year. When Christ died, this curtain was ripped from the top to the bottom without human hands. This miracle showed to all who saw it that God would no longer remain hidden away behind these pictures, but now every man could have full access to God through Christ by faith.
These are a few basic ideas that I am sure you can expand. Search a bit on the internet for Christian graphics, Christian resources or Christian design and you will find plenty of resources, some of them even free!
Jesus used miracles as proof of His divine authority, to give substance to His words, and also to demonstrate his other-oriented attitude by offering love and sympathy for mankind. Dr. Tyler gives several examples, healing of the leper and the Roman centurion's servant, the calming for the Sea of Galilee, the demon-possessed man, to name a few.