There should be HIDE IMAGE menu in your Magic Lantern...

Issue #567 wontfix
Former user created an issue

I am using Canon 550D with Magic Lantern successfully, i just want 1 feature to be added in ML. there should be (HIDE IMAGE) menu, Like:- make file hidden. as we take a picture shot, there should be some option to hide that picture, so that if someone press the play button that pic won't show in the camera's monitor (same as in Nikon D90) that picture should be hidden or hide for preview. I had used Nikon D90 and the HIDE IMAGE option was there.. i just want the same in ur Magic Lantern. Hope for the best..