Is deliberately imagining God, prophets, or angels—without believing in the correctness of the image—considered disbelief, and is that different from someone who experiences intrusive thoughts of images, knowing they are incorrect, and tries to get rid of them?

It is not permissible to imagine a specific image of Allah Almighty, because no mind can comprehend Him, and because "There is nothing like unto Him." Imagining Him is likened to comparing Him to creation. As long as the one imagining does not believe in the correctness of the image, it is not disbelief. However, one must cease these imaginings. The same applies to obsessive thoughts (waswasa). As for imagining prophets and angels, there is no harm in it, as long as it does not contradict established evidence regarding their descriptions. The best cure for obsessive thoughts is to ignore them and not dwell on them.