Flagged by Isaac Wilson:
Article Link: https://help.liferay.com/hc/en-us/articles/360028720632
Once you create a resolution, Adaptive Media automatically generates copies of newly uploaded images in that resolution. Images uploaded before you create the resolution aren't affected and must be adapted separately (see Generating Missing Adapted Images.
*Comment: "*Just a small note-- this sentence is missing its closing parenthesis mark."