I'll answer based on my experience. I see images with my eyes closed almost every time I go to bed. Most of the time it's just random flashes and it changes and it's just completely random and meaningless. However, there were a few times when I saw VERY clear, very detailed images of people and places I have never seen in real life and these images will move me in some way. That's when i know that I'm actually seeing something real.
Other times, I've had a dream about an event and it moved me emotionally. When I wake up from those sorts of dreams I can always remember it. Twice now I have had a very detailed, emotional dream that later on happened in real life. One of those was about the attack on Syria. I later saw photos on the internet that looked eerily like my dream. I completely believe I had visions in my sleep.
I'd say if you see it very clearly and it moves you emotionally, it's probably a vision. I often see people who are needing help, and I wish there was something I could do to help them.