It's not.

If you send something to someone and their device can read that thing, you should always assume that they can (technically) do anything with it because they have full control of their device. There is no way to prevent a skilled enough receiver to take a screenshot regardless of what scripts on the website says.

When it comes to cryptography and security, you should never assume anything about the behavior of your adversary. In this case, the device and the receiver are, from your prospective, the same party (because the receiver has full control of their device). If you don't want them to have a copy of the data, don't send it to them.

> The Nigerian price called and requested this be made open source lol

Why would a Nigerian price [sic.], which I assume you to refer to a scammer, want this to be open source?