[ChristianGeek]

Would flickering even be necessary? Why not just overlay several transparent GIFs/PNGs? It’s still hackable (so is the flickering solution), but you could also add in a few more tricks to make it more work for the hackers. For example, combine the layers dynamically into a single image with a separate HTTP request to retrieve the (random) positions of each layer within that image. (Just a thought...you could make it as simple or as complex as you want.)

[thedirt0115]

At that point, you could have your captcha-breaker wait for the page to finish rendering, screenshot the relevant portion of the page, and solve from there. Seems easier than trying to download and stitch together the transparent GIFs or decode the jumble of HTTP requests.

[lozenge]

That seems more like security by obscurity - as soon as somebody realises you are doing that, they can visit your site with headless Chrome and break it easily.