There are a couple of ways to make your images and it's up to you to choose the way you enjoy best. Try out both before settling onto one.
See The Cards image First in Your Mind
If you're clairvoyant, you probably see a lot of images in your mind. That's probably just how you think. When you create your own cards, it's the same. You'll meditate, journal about the experience, notice what important message came up and what you want to create on your cards. In that time you've probably seen the image that goes with the message. You may have even seen the image before the words came to you. This how many of my cards begin. I'll see the image, get it on paper and then write the message when I'm done.
Know the Message and Create The Image
Another way is to get the message first, write it out and then use corresponding images and colors to create the image. In this method, you're the researcher. Research what goes with the message you get. For example, if your message is around protection, you might choose colors that align with Archangel Michael, or the root chakra. You might use pictures of Archangel Michael, or things that remind you of safety and security. You could use a picture of the chakra system and highlight the root, a picture of the Sword of Truth, or a stone that symbolizes protection.