Ryan, I never got a response from you on this so I looked into the issue myself. It appears that the Web version of Twitter has an undocumented fallback to find the thumbnail for the Summary Card that other Twitter clients do not use. If “twitter:image” is set to a value, but that value is a URL that does not exist, Twitter web will fall back to “og:image” and attempt to use that URL instead. “og:image” is of course used by Facebook for its similar system of displaying meta-info about pages.
The reason this is a problem is that other clients, like Tweetdeck and the Web Widget, do not appear to use this fallback, creating the potential for bugs because the Web version will work as expected but the others will not.
Steps to see the problem:
- Create a web page that has a Tweet button, Summary Card info, and has “twitter:image” set to a URL that does not exist.
- Set “og:image” on that page to a URL that does exist and pointing to a valid thumbnail image.
- Tweet from the Tweet button on the page.
- In Twitter Web, look at the Tweet, click on Show Summary, and you’ll see the thumbnail came from “og:image”.
- In TweetDeck, look at the Tweet, you’ll see the card does NOT have the thumbnail.