How to fit a long sentence in a picture?

Question

Image processing

there is a random image with a certain width and height, let the image width be 400 pixels and height 690. I need to position the text on this image in the middle, I already have this algorithm.
What if the offer is long? For example, consist of 30-60 characters, etc.
The default font size is 60 pt. If the text is long, then you need to reduce the font size.
In my head, the algorithm is as follows: if the text consists of 50 characters, then you need to choose the appropriate font size for the capacity of all the characters in the image.

What are the other options?