Evo skin is really great! It can define the get_param_definitions() let users to make their own custom!
Now I want to make a option let users to choose an picture as their own background (or header picture), what I can do is add a param about 'type' => 'text' , and let user add an background picture url address, then I add some code to make it as the custom css!
It may be fine, but not perfect! For some pictures only users their own , and have not had an url address yet! They should first upload the picture somewhere , and copy the url address to use. This is a little bit troublesome, really! If we can have the upload function, users upload their own picture and we can get the url address to make the skin change! This is really comfortable!