Pictrure sizes to fit all devices

How can I add CSS to make images fit on iPhone, Android, iPad and Andorid Tablets? I am using the JotForm plugin within Buildfire for my app.

The image in your form fits perfectly on iPhone.

And so with iPad

By following this guide, your form should work perfectly and mobile responsive across different devices.

http://www.jotform.com/help/311-How-to-make-Forms-Mobile-Responsive

Thanks!