My thoughts are images that I have made.

It is because the thoughts you think you think appear as images that you do not recognize them as nothing. You think you think them, and so you think you see them. This is how your "seeing" was made. This is the function you have given your body's eyes. It is not seeing. It is image making. It takes the place of seeing, replacing vision with illusions.
This introductory idea to the process of image making that you call seeing will not have much meaning for you. You will begin to understand it when you have seen little edges of light around the same familiar objects which you see now. That is the beginning of real vision. You can be certain that real vision will come quickly when this has occurred.
As we go along, you may have many "light episodes." They may take many different forms, some of them quite unexpected. Do not be afraid of them. They are signs that you are opening your eyes at last. They will not persist, because they merely symbolize true perception, and they are not related to knowledge. These exercises will not reveal knowledge to you. But they will prepare the way to it.
In practicing the idea for today, repeat it first to yourself, and then apply it to whatever you see around you, using its name and letting your eyes rest on it as you say:

This ---- is an image that I have made.
That ---- is an image that I have made.

It is not necessary to include a large number of specific subjects for the application of today's idea. It is necessary, however, to continue to look at each subject while you repeat the idea to yourself. The idea should be repeated quite slowly each time.
Although you will obviously not be able to apply the idea to very many things during the minute or so of practice that is recommended, try to make the selection as random as possible. Less than a minute will do for the practice periods, if you begin to feel uneasy. Do not have more than three application periods for today's idea unless you feel completely comfortable with it, and do not exceed four. However, the idea can be applied as needed throughout the day.

- Jesus Christ in A Course in Miracles, Lesson 15