Hi!
Does this issue persist all the time?
Does anyone else have the same issue in your organization?
Can you see the picture that uploaded in Teams chat? In other words, does this issue only happened in Teams channel?
Considering these pictures are uploaded to Teams channels, we recommend you check if you can see pictures normally in the SharePoint online.
Besides, you can try to clean the client cache to see if it can be fixed.
https://www.onmsft.com/how-to/how-to-clear-your-microsoft-teams-cache-on-windows-10
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