I am developing a extension and I've to add an icon on images of products having specific tag "app_product". Yes, I know that we can do this task by modifying view.phtml and list.phtml but I think this approach is theme dependent. What I want; when I enable my extension the icon will be appeared and when I disable my extension, the icon must be disappeared. And I've to this task independent of theme. Please help me to figure out this issue.
And Thanks in advance.