Settings in Site icon & sharing, on the theme's settings page (Appearance › Themes › Configure Theme).
Site icon
The Site icon appears in browser tabs and bookmarks, and as the app icon when a visitor adds the site to a phone's home screen. Use a square PNG of at least 512 × 512 pixels. The Configure Theme page accepts PNG, JPG and GIF files up to 1 MB; a PNG icon is usually far smaller.
Browsers keep a site's icon for a long time. After changing it, reload the page, or open the site in a private window, to see the new one.
Sharing image
The Default sharing image appears with links to your site on social media and in messaging apps, when the shared page has no image of its own. Items, files, collections, exhibits and exhibit pages use their own first image; the home page, Simple Pages and browse pages use this one. A 1200 × 630 pixel image (PNG or JPG, up to 1 MB) works best.
To change or remove an uploaded image, click Change beside it, then choose another file, or leave the field empty and click Save Changes.
Search engine and sharing tags
Every page gets these tags (in themes that show Add search engine and sharing tags, as long as it is on, the default):
- link preview tags (Open Graph and Twitter cards): title, description, image and the site's title;
- a canonical address on item, file, collection, exhibit and Simple Pages, so search engines treat every address of a page as one page.
Whatever the setting, every page also gets a description: the item's, file's or collection's Description, the exhibit's description, the first text of an exhibit page or Simple Page, or else the Site Description under Settings › General. The author and copyright lines under Settings › General become tags too.
The address bar on phones takes your header color.
If a plugin adds its own link preview tags, turn the setting off so they are not added twice.
The description comes from your content, so keeping item descriptions and the Site Description up to date improves how your site appears in search results.