This is obviously a web app, so it all depends on the use of your web framework (probably just a simple CGI script, I guess?) and also on how exactly you want those pictures to appear.
You probably want to display some sort of matrix of images on the page to represent the field of plants, starting with "empty slot" images and then replacing them with alive or dead plants one by one, right? For that you need to create the matrix with unique IDs for each image source in your html output. Each time a question is answered you need to figure out the ID of the image that will be affected and change it's image source to point to an image of "empty slot", "dead plant" or "alive plant" accordingly.
If this is handled with a web form then you also have to think about preserving the state of the field, i.e. the currently displayed images in each slot. You could do this with hidden form fields.
A better and more modern solution would employ AJAX techniques to update pictures on the page without reloading it and some sort of web programing framework like CGI::Application or Catalyst.