nikalmus/img-block

what this app does:

In the context of this app, mining involves trying different nonce values until one is found that, when combined with
Exif data of the image and the previous block's hash, creates a hash with two leading zeros.
These elements are concatenated into a single string, which is then fed into a cryptographic hashing function SHA-256.
To start the blockchain, drag and drop the first image and click on 'Mine.'
When Hash is produced, Prev Hash of the next block is automatically set.

You can follow the same process for the other images.
Because the hash function is deterministic, any modification to the Exif data,
previous block's hash, or nonce would produce a completely different hash value.
The remaining steps show that if a bad actor alters a past transaction, all subsequent blocks must be re-hashed.
To experiment with Bad Actor mode, click on the 'Bad Actor' button.

An alrtered image of Vermeer's "Astronomer" appears in the image repository
In Bad Actor mode you can drag and drop an image onto a previously hashed block.
This will effe ctively change the exif data.

At this point a new Hash must be found.

If the altered block is rehashed, Prev Hash of the next block will no longer match the Hash of altered block.

The process is intentionally cumbersome.
After clicking the "Mine" button, use the copy icon to save the new Hash to the clipboard.
Then click on the Prev Hash of the next block.

Paste the new Hash of the previous block from the clipboard,
click "Done", and click on "Mine" button to re-hash the current block.
A bad actor would have to repeat these steps for all subsequent blocks.