Html and CSS image uploader -

i'm trying convert image bubble(below), can use upload images when user creates account, example when user hovers of image bubble display "upload profile image" , when user clicks it, should prompt them upload image. can push me in right direction achieve this?

i'm assuming know how image uploading works, if not, please specify. in css, have tried:

form{     position: absolute;     opacity: 0;     /* you'll need fine-tune part */     top: 50px;     left:50px;     /* if want, can add transition on opacity */ }  form:hover{     opacity:1 }