Automatically update an area in an image with another image (good for advertising)

Hi all,

I hope i'm not overthinking this or missing an existing solution, but if I do: please let me know :-)

Quick sketch of the situation where it comes in handy:

• I'm about to run an advertisement on a website
• I want to see how it looks like
• I create a design in favourite software
• 2nd monitor shows a full screen picture of the website
• My advertisement design is added into this picture

What I do now:

• I save the full website to an image using Chrome's screen capture function
• I load the image in photoshop
• I place my design into this 'screenshot'
• On every alteration I do I save and repeat the step above.

How it could work:

1. Start an app
2. Load an image/screenshot (or enter an URL to screenshot)
3. Reserve an area in the image
4. Add an image to this reserved area
5. Every time the image is updated, update it in the "screenshot"

Do you see the benefit in this?