You can customize previous_post_link like this
previous_post_link("https://wordpress.stackexchange.com/questions/157503/%link",'<img src="https://wordpress.stackexchange.com/questions/157503/link_to_image"/>');
You can customize previous_post_link like this
previous_post_link("https://wordpress.stackexchange.com/questions/157503/%link",'<img src="https://wordpress.stackexchange.com/questions/157503/link_to_image"/>');