We have the description in revelation of Jesus. Look when I pray sure I can picture someone who I am praying for or what ever, but I caution against using to much imagination, like trying to picture them changing is some way.
However when you consider God saying, don't make images and do not bow down to them, I think we find ourselves in danger attempting to create an image of God even in our imagination. Comparatively we have Jesus saying for example do commit adultery, but who ever looks on a woman and lusts has already committed adultery. So we take caution not to look at women inappropriately, or too long, or any other way that couldd lead us to think inappropriately when looking at her.
If we apply the same concept to, do not make any images and do not bow down to them, then I think you find yourself in dangerous territory attempting to form an image of God in our imagination, especially when praying. Because now you are bowed down to the image you have created in your imagination. Not that we don't, when reading some descriptive passage, have an image in our mind of what is being described.
The point is the command of God. So while we aren't under a mandate of the ten commandments, they do inform us of what sin is, and where the dangers are.