Speckles appearing on black images

Hi,

Im working on https://www.culturedcarpbaits.co.uk and ive noticed today that all of the images with a black background, inlcuding home page and including photos in the gallery have white speckles, like stars.

This has only happened today, was fine yesterday. ive checked the site in multiple browsers and ist the same.

Can anyone help explain what has happened and how i might fix it?

thanks

nik