The mask, the tool of the hero and villain alike, yet so under valued by most. It is not just a way to hide someone's secret identity, but it is also a way to help communicate an identity as well
Bright colors that demand attention, a mask that had best be worn by someone with the powers to match...
A themed mask should not only match a person's power set, but it should also connect to that individual's stated mission... It would be a bad idea for a villain calls himself 'The Carnivore' to blow up steak houses while declaring the virtues of being vegan (As if there were any)
Simple, classic disguises can still be a good choice, but not everybody has the right attitude to make it really 'work.'
In an emergency, just about any way to hide an identity can be used, but a Hero especially needs to be careful of what message they might be sending.
Grade: 23897 points. I think the message you are sending with the last one is "I'm a spy with bird flu"
The key to fooling people is not in hiding your face. Brains are lazy and most people identity others by remembering 'key markers.' These are things that stick out in the mind.
Example: at the start of the semester, I never went out in public without a black fedora. Professors, the people sitting next to me all thought of me as 'hat girl.' After a few weeks, I took off the hat. I was nearly marked absent, the number of double-takes from people next to me was amazing. The next day I put the hat back on. A few people I pass in the hall asked were I had gone the other day, the professors didn't stumble through roll call, and my classmates smiled and pointed at the hat. Disguises are about giving people something else to remember instead of what the police need to draw a composite. If the 'key marker' is stands out and can be easily changed - jackets, false moles, facial hair, sunglasses - moving between identities is simple.
Common accessories can allow a hero to go from 'terrified civilian' to 'beat down mode.' Testimony at the scene should be a version of "The chick with the hat and bandanna went all Rambo!" Pictures are general taken after the bad guys burst in. So the second image is what should be on the news.
What you don't want to do is have a starting look that draws attention from the beginning. While this hoodie/ball-cap combo has great concealment, it screams, "person hiding something! OVER HERE!" The icon on the shirt does pull the eyes away from the face, but this sends a dangerous person vibe that people will remember.
Speaking of 'vibes,' personae are as important as the clothes. A retro hippie stands out in people's minds. They remember the crazy jacket, sunglasses, and weird language more than my actual face and bodyshape. In the right situation, getting attention is a good disguise. When I slip out of the fringe jacket, tie-dye, and wear my hair loose, I've vanished into the crowd.
Important Note: Facial and body matching software is almost impossible to fool. Unfortunately, cameras are all but impossible to avoid whether in or out of costume. The effectiveness of any disguise is limited to people at the scene and low quality photos. This is still a good thing, but I foresee the standard hero 'look' soon favoring more bulky/concealing elements to combat this new technology.
Grade: A pair of lifts for your shoes to try to fool that software
So I'm just gonna link all the images because it's gonna be too hard to do this one by one (i.e. I'm lazy ) But essentially, when making a disguise you have to think of covering up recognisable features, or draw attention away to something you can easily change (i.e. a mask). Furthermore, posturing and facial expressions can change a lot about a person, including mucking up description of height, age, possible occupation, etc. Finally, if worst comes to worst, they won't expect a guy to be in a dress.