You can easily add a background image to your form, but that background will apply to all pages, and therefore all questions.
A background image cannot be set for individual questions. However, you can upload an image to the body of your form and place it above or below a question.
You can add a background image to your form by following these steps:
In the form editor, select Theme → UI Elements → Background.
Select "CHOOSE A FILE" under "Background Image" and upload your image.
Using slash commands
On a blank line in the form editor, type
/image and select "Image" (not "Image Upload") from the dropdown menu.
Then follow the prompts to upload your image.
Continue to Step 4 below the next section.
Without using slash commands
In the form editor, select the line on the page where you want to add an image.
Choose the "Add picture" icon to the left of that line.
Follow the prompts to upload your image.
Once the image is uploaded, you can access a range of formatting options by selecting the image.
If needed, you can edit your image within Paperform.