How do I set a global variable when a button is clicked through iframe?

Im displaying an image carousel through an iframe on my hosted website. I have a button below the image slider and when it is clicked I would like to know what image is currently being displayed. The images are displayed via php with bootstrap carousel. Thanks for reading.

You will need to present the file being viewed as a variable from your PHP script.

Then this thread should hopefully get you the rest of the way...

https://www.construct.net/en/forum/construct-2/how-do-i-18/pull-variables-php-page-40884?kws=return%2bphp%2bvalue