To be added somewhere sensible ... tips care of Corey Griffith:

http://betterposters.blogspot.com/2019/02/top-tips-for-twitter-posters.html

Another link on social media image sizes:

https://sproutsocial.com/insights/social-media-image-sizes-guide/#twitter

• Minimum to appear expanded 440 x 220 pixels (a 2:1 ratio).
• Can tweet up to 4 images at one time.
• Can edit images if tweeting from Twitter iOS or Android app.
• Maximum to appear expanded 1024 x 512 pixels.
• Appears in stream collapsed at 506 x 253 pixels on desktop.
• Maximum file size of 5 MB for photos, and 5 MB for animated GIFs on mobile and 15 MB on web.