...that our brains reacts on our faces on the basis of the most often seen people's faces. That's why over the years people living in a long-term relationship they look more and more similar to each other, and adopted children as well resemble their foster parents.
When your activity, your work which is being reflected on your face seems less strenuous, then you will more likely to hear "you look good" phrase from others. However if you aren't as lucky, you will less often receive commendation and you quickly attach to aging in place of laughter. Unfortunately your brain records the negative information as well and starts aging your face according to these negative expectations.
...application warns you in a pre-set times and then displays the image you've selected.It is important to choose an image where you look the best. If you cannot find such picture, you can choose someone else's image, for example an actor who somewhat resembles you. When the image appears in the screen, imagine, the screen is a mirror and the current person in the mirror is you. You have to concentrate, otherwise it will not work! Let your mind know that you look like the person in the picture!
The effect wont appear soon. Moreover, even in the long run you will not notice as you have not noticed the change of your facial expression. It makes the striking difference when you are looking at old pictures. However in a couple of months you will notice that more and more people will praise you, or when someone unknown to you would have to guess your age, he would say you look younger.
If you think it will not work for you, than indeed it wont work for you. Don't even try, useless!