Displaying an image instead of text using <?php the_category(‘,’) ?>

I’m wondering how I can replace <?php the_category(‘,’) ?> within the loop so that I can show an image instead of a text link?

Wen I use the <?php if(is_category() ) { ?> function, it gives me a syntax error – but I think I’m on the right lines with that, but just not using it properly!

Here’s my site – https://willvbcfc.com/index/

And I want corresponding images for both my Design and Thoughts categories to show at the top of the red box entitled #postblock instead of the text.

Cheers!