How to prevent robots from making a POST request?

Question

JavaScript

Hi all.
There is a file upload form. This form does not have a submit button. When a file is specified by the user, the file is automatically uploaded to the server (event + submit to a hidden frame).
Without any user registration - this is the key point!
The problem is that robots shove images into this form and successfully upload more than 100 images per day, which are cleaned by the cron handler.
How to prevent robots from making a post request?
I tried dynamically using JS to connect the action to the form - it did not help. Apparently, modern spam systems perfectly understand JS and it is not possible to distinguish a "browser" from a robot.
PS Do not offer captcha - it is for the main form on the page. Doing a captcha for uploading a file is not an option at all.

Answer 1

Have you heard about captcha ?
The easiest for users is reCaptcha (just click on the checkbox)

Answer 2

Check on the server what came in the request, and if the file is not interesting to the server, then do not save it.

Answer 3

And how does the cron handler understand what it needs to clean?

Answer 4

Are robots really entering through the site?
Without CAPTCHA, they can send requests directly!
Do you have a unique "ticket" in the form?
Do you check the client for presence on the site when uploading a file?
Well, check right away whether there is something to bind to (in the sense of whether there is a TICKET for creating an ad that is tied to a TICKET for downloading).