REPLACe
<img src="<?php bloginfo('template_directory'); ?>/art/pic_ourwork.jpg" alt="SFData" />


WITH
<?php
                       if (has_post_thumbnail()) {
                           the_post_thumbnail();
                       } else{
                           ?>
                           <img src="<?php bloginfo('template_directory'); ?>/art/pic_ourwork.jpg" alt="SFData" />
                           <?php
                       }
                   ?>