How can WhatsApp show me an image/video if I didn't download it to phone?

If I send an image/video via WhatsApp and the other person doesn't download it, how can he still see the image as a blurry image? From looking through the app's database, I found out that the local path of the image that was downloaded is located in the thumb_image column in the messages table. However, if the image is not downloaded, I don't have any information about the local path. Does WhatsApp store that image as temporary image data on the device?