Additional file-related features and issues within Microsoft Teams for business
Hi Eric,
Greetings.
Thank you for raising your concern in this community.
From what I know, this is a known issue. As of know, please do use teams on the web to download the pictures and save as https://teams.microsoft.com.
Another way will be to right-click the image and open it on the browser. Then right-click the image in the browser and choose Save Image as
Another workaround you can try, use the Files tab in your channel. And download the image directly from there.
There is a current feedback section for this feature, please take the time to give a vote Teams renames and converts images when downloaded from chat · Community (microsoft.com)
Thank you for your time and understanding.
Kind regards,
Mac