How add an icon or a little image before the Gallery page title if it is possible ?
I tried <img src="test.png"> in the Title field Page without success.
Titles, labels and descriptions don't support the <img> tag unfortunately. Even if they did, it would be very clumsy to try to align the image with text. Optionally, you can use font-awesome font icons, with the benefit that they will inherit the font size and align perfectly. https://fontawesome.com/v4.7.0/icons/