I’ve installed the timthumb code in its own directory within my theme.
I then have a field within my repeater called image
Finally, I have a line of PHP ($theme_path) which I call from my function file. This is simple the path to timthumbs files like so:
<img src="<?php echo $theme_path; ?>timthumb/timthumb.php?src=<?php the_sub_field('image'); ?>&w=618&h=298&q=100">
That should get you what you need. Hope that helps