Twitter Card (photo) is showing error in the validator tool, but all single tags are valid

Question

I'm trying to add twitter card support for our own image server. Currently the meta tags are like:

<meta name="twitter:card" content="photo">
<meta name="twitter:site" content="@FotoDish">
<meta name="twitter:creator" content="@FotoDish">
<meta name="twitter:title" content="FotoDish">
<meta name="twitter:image:src" content="http://img.fotodish.com/upload/534d5a08a15537a840cafe8e">
<meta name="twitter:domain" content="fotodish.com">

as in http://fdi.sh/i/534d5a08a15537a840cafe8e .

However, the validator tool shows error, while all single items are valid.

What is the issue?

Thank you!

Answer 1

I eventually find the reason... It was a little tricky and Twitter didn't say anything about it in any docs, which is ....

You need to set the Content-Type of the image correctly.

In my situation, I used Amazon S3 and Cloudfront for image storage. When I uploaded the images to S3, I didn't set the MIME type so S3 used application/octet-stream as the default value. In this case, the images could be shown in an img tag correctly, but would not be treated as an image by Twitter bot.

So I just reset the Content-Type of all the images to 'image/png' (or whatever they should be) and everything was all good.

P.S. Also make sure that you have your robot.txt allow Twitterbot to access.