I don't think this is possible in pure html. You will need to add some amount of Javascript. This can either be done in a separate file linked to your html or inside tags.
Regarding the specifics of what JS you need I have no idea. Start with steps, first setup the layout using HTML and then add functionality step by step. In this case something like:
- Start with two buttons (one to open image, one to take image)
- Add functionality
- Open image with placeholder text
- Make the text over image editable using input forms
It's best to work step by step and ask specific questions to help you complete each step.
These links may help:
Access camera from a browser
Text over image in javascript and css