How can I include a background image in the form as shown in the image?

Looks like you're giving this a try on this form:

https://www.jotform.com/83007673489870

There's no way to adjust the opacity of a background image through CSS. Well, there's a workaround but that would require you to have access to the HTML content (which you don't have).

My recommendation is for you to do this outside JotForm. Download your background image, or if you have it saved in your PC, open it with an image editor that allows you to adjust the opacity (e.g. Photoshop). From there, change the opacity > save the image > then re-upload that adjusted image as your new background.

Ok..

Thanks for your answer.