Hi Erkan,
Welcome to the Atlassian Community!
Could you please provide a specific endpoint you're trying to use to add an image to a card? I'll try to replicate the issue and either try to resolve it with you or escalate it to the development team.
Please make sure not to share any personal data (such as API key and token) in this post. You can also submit a ticket at https://trello.com/contact for us to look into this further or
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