Help to publish an images list

Good morning. I need to publish on a page all the images present in various categories (all gathered in the main category “gallery”) without having to create a content type and a model content, as I load the images directly from the Assets. Also I would like to put filters for the various categories selectable by the front end user. How can I do? I guess I have to create a widget but I don’t know how to write the code.