There are 2 ways to do this. 1) Remove the text box and button and add the image as div tag background and inside div tag add form 2) Add this image as it is and add a text box around it and css button to link them.
Here is how I would approach this. 1) I would make the image a background using CSS. 2) Then create the form in HTML. With some styling you can position the fields over the input field image. Remove the border from the input/text field. 3) For the submit button I would make that it's own image With your image editor of choice remove the submit button from the main image and save the button as a separate image file. Then where the button was clean it up using the background green. Then make the submit button and image button.