Customize background of form and field placement

Is there a way to place a background image and put form fields on top of it? I have a diagram that needs labeling and it would be helpful to be able to place the fields next to the part that needs a label.

Thanks!

Would I also be able to place fields exactly with CSS?

You can define a background image with CSS.(API & Code -> CSS).

Ex:

.view_id {
  background-image: url(/*your image url here*/);
  }

you can further play with more properties like background-size, background-repeat, background-position. etc

for more details : http://www.w3schools.com/cssref/css3_pr_background.asp