Hope I can help here, as this is the only way I've found to do it.
1. Go to Photographers Member List
2. Find your portfolio there
3. On the the left side there should be a link saying MANAGE PHOTOS and click it.
4. on next page find the Category Box and choose a category.
This should take you to all photos in that category. You should find buttons right of the photo where you can delete it.
Hope all this helps.
