php - How to write the same route to a file from differents files located on different folders -

imagine have following folders , files:

• folder_a/
  • file_a.php
  • folder_a1
    • img_a1.png
  • folder_a2/
    • file_a2.php

is there way can write 1 route img_a1.png no matter if on file_a.php or file_a2.php?

this i'm doing now:

to access img_a1.png file_a.php:

 <img src="folder_a1/img_a1.png"/> 

to access img_a1.png file_a2.php:

<img src="../folder_a1/img_a1.png"/> 

i don't understand goals but, answer may fit requirement:

       define("img_dir ","c://xampp/htdocs/project/folder_a/folder_a1/"); 

now write code :

<img src="<?= img_dir ;?>/img_a1.png"> 

now don't need specify directories in every php file in different categories

i hope can use ^_^