An OG image is the picture that appears when somebody shares your website link. OG is short for Open Graph, the set of tags that tell WhatsApp, Facebook, LinkedIn and your phone messages app which picture, headline and description to show in the preview card.
Why it matters more than it sounds
Word of mouth for a trade usually travels as a shared link these days. Someone posts in a village Facebook group asking for a roofer, and a neighbour pastes your address in. What everyone in that group sees is your OG image, not your homepage.
With no tag set, the sharing app guesses. It usually grabs the first image on the page, which might be a logo on a white square, an icon, or nothing at all, and the link goes out as a grey box with a web address in it.
What to put on it
Make it 1200 pixels by 630, the size Facebook's own sharing documentation asks for and the one the other platforms crop to. Facebook on sharing images, read 15 September 2026. The full specification is on ogp.me if you want the detail.
Use one good photo of your own work, your business name in large type, your town and your phone number. Keep the type big, because most people see this card at about the size of a stamp on a phone screen. Do not fill it with small print.
A worked example
A drainage firm in Plymouth gets a mention in a local Facebook group. The link preview shows a photo of a cleared drain, the firm name, Plymouth, and the number.
Two people in that thread ring the number straight from the preview without ever opening the site. That is the OG image doing the whole job on its own.