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LimeSurvey version: [see right hand bottom of your LimeSurvey admin screen]6.69
Own server or LimeSurvey Cloud:LimeSurvey CloudS
urvey theme/template:bootswatch==================
I would like to ask, in the questionnaire, if the survey is filled out on a mobile phone, the images cannot adapt to the phone's screen size and will exceed the boundaries of the question boxes, as shown in the image below. How should I address this issue? 

Hi, this is not really surprising.
You use absolute values for "width" and "heigth".

I used this
(as LimeSurvey is based on bootstrap, you may read the bootstrap documentation.)
[url] getbootstrap.com/docs/5.3/content/images/ [/url]

<img alt="" class="img-fluid" src=" www.mafoservice.de/userfiles/Boot001_gross.jpg " style="width: 70%;margin-left:15%;" />

and get
 

 

Joffm