Make feed grayscale

Hi!

I’d like to make the feed I have at my page either grayscale or alternatively insert a “permanent mask” (like a white “filter” to make the images look paler all through, or something like that).

Is this possible to do?

I have no earlier experience with coding, so please be pedagogic if the answer involves any CSS-hacks or similar xP

Cheers!

/Max

The page I need help with: [log in to see the link]