It’s very easy to find pictures on the Internet and copy them to use on your own website. However, in doing so, you could easily be infringing copyright, and the owner might seek compensation.

Paul Clarke has written a useful guide especially for w4mp on publishing pictures and avoiding rights issues, which you can find here: https://w4mp.org/w4mp/w4mp-guides/support-in-your-job/publishing-pictures-and-avoiding-rights-issues/

There’s also some information at the end about what to do if your MP’s office receives a Copyright Infringement Notice.