welcome to talk.typo3.org. Please stick to English with your question in the future, so more people can help your with your problem.
I need more information about your setup.
As your problem is located in the frontend, are you sure that the default CSS of TYPO3 is loaded on your website? TYPO3 provides own CSS which could be not loaded or not found.
If you have own CSS you need to look up if this is changing the image behaviour.