What makes a share image work
The share image is the biggest part of a link preview, so it decides whether people click. Use 1200 by 630 pixels, large text (it is often shown small), high contrast, and your brand. Keep important content away from the edges, where some platforms crop.
After uploading, set the image in og:image and twitter:image (the Open Graph generator writes the tags), then check the result with the social preview checker.
Questions
What size should an OG image be?
1200 by 630 pixels, an aspect ratio of 1.91 to 1, under 5 MB.
Is my logo uploaded anywhere?
No. The image is drawn in your browser.
PNG or JPG?
PNG for text and flat colours; JPG for photos. This tool exports PNG.
Why does X show an old image?
Platforms cache previews. It updates after their cache expires, or when the URL changes.