How to show randomly generated text and image from a .txt file?

Here is my code that generates random texts from the random.txt file inside a input field.

<?php
 //Path of file
 $myFile = "random.txt";
 //Read file from array
 $lines = file($myFile);
 //Get number line of file
 $lineTotal = count($lines);
 //Remove 1 line (start from 0)
 $count = $lineTotal-1;
 //Get casual number
 $number_casual = rand(0,$count);
 //Print line 2 ([0] = 1 ; [1] = 2 ; ...)
?>
<input name="accesspin" style="width: 300px" value="<?php echo htmlentities( $lines[$number_casual] ); ?>" size="36">

Here is the random.txt file:

USA
UK
Canada

I want to show random pictures above the input field:

<img src="A random pic"alt="Flags" height="42"width="42">

<input name="accesspin" style="width: 300px" value="<?php echo htmlentities( $lines[$number_casual] ); ?>" size="36">

And the random.txt will look like this:

us_flag.jpg
USA
uk_flag.jpg
UK
ca_flag.jpg
Canada

I want this PHP code to randomly show a flag picture above the input field and the country name under the flag picture's file name in the txt file to show inside the input field.