Easiest and safest way to do this without modifying the framework code is to by inserting the following Custom CSS in the file custom/custom.css or in the Custom CSS tab of the theme options panel –
.type-portfolio .image-info { padding: 10px 0; } /* Increase the height of hover when categories are not shown */
.type-portfolio .image-info .terms { display: none; } /* Hide the categories */