Your promo-tweets are showing the same image day after day.
One of these fixes will solve or explain your problem in 99% of the cases.
1. Turn off the twitter toggle in your settings and turn back on.
2. Check your Auto-promote redirect field in your settings. If you have entered a URL in this field, you will not see a new image for each promo-tweet.
3. Check that you have the full URL of your paper saved in the tweet, including the prefex http:// i.e. http://paper.li/yourpaper.
4. Be aware that if you include any other URL besides your paper URL (for example: a URL shortener or a snip.ly for your paper), the most recent "meta data" for your paper is not being sent to Twitter. This will result in Twitter displaying an incorrect image for your paper on most days. However, if you still wish to include a URL other than your paper's URL, be sure to include http:// in front of your URL.
In order for Twitter to pull the correct image, your paper URL must include the edition id.
A URL which includes an edition id looks something like this:
If you have not edited the default URL in your tweet, the paper.li platform will automatically add this unique edition id to your paper URL at the time of the tweet.
If the edition id is not appearing in your tweet, the URL for each auto-tweet is not unique. The first time Twitter pulls the image for that paper URL, the image will be correct and will be taken from the headline article.
But the same image will repeat for up to 7 days. Why? Because once Twitter captures the image for a URL, Twitter will continue to show that image until the data in its cache (temporary storage) expires. By including the edition id in the post, your paper URL is unique and Twitter is forced to check for the most current image.