Problem with adding <img> tag to the code

The user uploads a plain text file with a decimal value(eg. 36.81) on each line of the file. I have to upload this, open it and make a histogram out of it. I have done everything but cannot do it with the help of the img tag which I am supposed to do. Here is the code I have written as of yet:

Code for uploading the file and feeding all values in an array

<?php
if(($_FILES['img'] != '') && ($_FILES["img"]["type"] == "text/plain"))
		{
			move_uploaded_file($_FILES['img']['tmp_name'], "upload/" . $_FILES['img']['name']);
		}
		else
		{
			die ("There is an error in your upload. <br> Either the file is not a .txt file or you havent selected a file") ;
		}
		$data = array();
		$fp = @fopen ("upload/" . $_FILES['img']['name'], "r");
		if ($fp)
		{
			while(!feof($fp)) 
			{
				$this_line = fgets($fp);
				$this_line = chop($this_line);
				array_push($data,$this_line);
		}
		
		fclose($fp);
		}
echo("<img src='histogram.php?' alt='None' />");
?>

Code to create a histogram using the $data array(histogram.php)

		$sum = array_sum($data);
		$num = count($data);

		header("Content-type: image/jpeg");
		
		$height = 700;
        $width = 50*$num;
        
        $im = imagecreate($width,$height);

		$white = imagecolorallocate($im,255,255,255); 
        $black = imagecolorallocate($im,0,0,0);
		$red = imagecolorallocate($im,220,0,0);	

        imageline($im, 10, 5, 10, 600, $black);
        imageline($im, 10, 600, 200*$num, 600, $black);
    
		// Now plot each column
        $x = 15;   
        $y = 600;   
        $x_width = 20;  
        $y_ht = 0; 
       
        for ($i=0;$i<$num;$i++){
        
          $y_ht = $data[$i];//$sum)* $height;
          
			  imagefilledrectangle($im,$x,$y,$x+$x_width,($y-$y_ht),$red);
              imagestring( $im,2,$x-2,$y+10,$data[$i],$black);
              
          $x += ($x_width+30);  
        }
        
        imagejpeg($im);
		imagedestroy($im);

At present, it works because both the pieces of codes are in one php file. But I need to have them in this way and they don't work because the data array cannot be read by histogram.php. Anyone knows a way to do that?