>Does this allow Twitter to change the picture after it was posted?
YES.
You'd change the file on OF website, keeping same filename, then force Twitter to flush its cache to ensure showing of new image, by using the Twitter Validation Tool.
>Does this allow Twitter to change the picture after it was posted?
YES.
You'd change the file on OF website, keeping same filename, then force Twitter to flush its cache to ensure showing of new image, by using the Twitter Validation Tool.