It's all about character.
Back when I taught teen Sunday school, at one point I used coins as an illustration. It's only really necessary to have two coins for the illustration: pennies and quarters are useful since the images on them are more readily recognized.
If I hold up a penny, ask someone to look closely at the image, then ask "Who is that?", the answer comes back: Abraham Lincoln. If I do the same with a quarter, the answer comes back: George Washington. And with decent likenesses, we can answer questions from looking at them. "Who had a beard: Washington or Lincoln?" We can see that it's Lincoln. "One of them had a wig with a long strand of hair in back. Which one?" We can see that it's Washington.
And then: I place the quarter on my thumb, flip the coin so that it spins in the air many times before I catch it, slap it face-down on my other arm in traditional coin-toss fashion, and with the coin still covered I ask one question: "Is George Washington dizzy?"
At which point they laugh but they get the point. You can tell a lot from an image. The better the image, the more you can tell. But the image is separate from the original. We could use the same quarter in a coin-toss all day, and it would never make George Washington dizzy.
The word "character" is originally a Greek word, used in engraving and in minting coins which were made by stamping an impression. In this sense, "character" is used in a famous passage in the New Testament, discussing Jesus' relationship to God: "Who being a reflection of his glory and an impression of his substance" -- or in the words of a more familiar translation, "Who being the brightness of his glory and the express image of his person ..." (Hebrews 1:3).
If you have ever spoken to someone who is not used to the ideas of Christianity, sooner or later we are called to explain what we mean about Jesus and God. "Whoever has seen me has seen the Father," Jesus told his disciples. And yet when Jesus died on the cross, God did not cease to exist. Much like, when I tossed the coin, George Washington was not dizzy. The analogy is imperfect but it makes its point.
We can look at the image and learn about things unseen. It is often the purpose of an image: to make known or make present things that are not seen. The better the image, the more clearly we see what we could not otherwise see. Jesus was born in a certain time and place in human history; there was a time before he existed. Much like the coins were minted long after the time of the persons represented. Yet it is a key part of Jesus' essence: whoever has seen him has seen the Father.
That is my two cents' worth for the day.