View a webpage on a mobile phone or iPad

The site is almost ready, but I still have a few questions.
The homepage displays a full-size image with text, but on a mobile phone, iPad, or tablet, the image does not appear in its entirety (see attachment). In other words, it doesn't scale down automatically. Do I need to upload a smaller version of the image for mobile phones and tablets, or can this be adjusted via the settings?
I intended to include an attachment, but it seems I am unable to do so at the moment.

Please provide the URL of the affected website and post screenshots showing the specific image you are referring to. Additionally, please let us know which devices are experiencing display issues or failing to respond correctly in terms of responsiveness.

The url:  www.rumani2.be/