What are "control a library" and "how to it"? The terms are quite vague, a more precise description of your goal would help.

I apologize for being vague. Let me see if I can be more specific.

I am using a ping sensor connected to an arduino board. I currently have it set up so processing is reading the serial data coming from the sensor and the arduino. What I am trying to do is assign an image to a distance.

So at 1 in - a.jpg would be triggered
      at 2 in - b.jpg would be triggered
      at 3 in - c.jpg would be triggered

and so on.

I have done this with audio files using the Minim library but I haven't been able to get images to work.

Thanks for your help! I am really new at this .

The code I am working with so far looks like this. It reads the ping info and tries to call on the .jpg but processing says that it 'could not find method to load Fox_01'.

Thanks!

1. 
   
   import processing.serial.*;
   import processing.video.*;
   
   Serial myPort;
     
   
   PImage img1;
   PImage img2;
   PImage img3;
   PImage img4;
   PImage img5;
   PImage img6;
   
   
   void setup () {
   
   size(640, 480, P2D);
   background(0);
   noStroke();
    smooth();
    
    PImage img1 = loadImage("fox_01");
    PImage img2 = loadImage("fox_02");
    PImage img3 = loadImage("fox_03");
    PImage img4 = loadImage("fox_04");
    PImage img5 = loadImage("fox_05");
    PImage img6 = loadImage("fox_06");
   
    
     println(Serial.list());
     myPort = new Serial(this, Serial.list()[1], 9600);
     myPort.bufferUntil('\n');
       }
   
       void draw () {
     
       }
   
       void serialEvent (Serial myPort) {
   
       String inString = myPort.readStringUntil('\n');
   
       if (inString != null) {
       inString = trim(inString);
      
       float inByte = float(inString);
       int Images = int(inString);
   
       println(Images);
   
   
   
       if ( Images < 5 )
       {
       loadImage("fox_01");
       delay(33);   
   
       }
   
     
   
       else if ( Images > 50 )
       {
       }
   
       }
       }
   

OK, much better!
You make an error lot of newbies did before you... You define/declare global PImage variables, which is fine, but when loading them, you redefine new (local) PImage variables, of same names than the global ones, so masking them, and their value/content is lost at the end of setup()! The cure is simple: drop the 'PImage' part inside setup(). So you use the declared variables (initialization) without re-declaring them.
Note: as soon as you have more than three variables with same name (and number), you should start using arrays and loops!
Also the loadImage() inside serialEvent() is useless if you don't assign the result (and avoid loadImage outside of setup() in general). And avoid using delay() unless you have good reasons for that (most usages I saw were inappropriate).