I am interested in adding photos to either existing plants in the database, or introducing new plants to the database. I'm not sure how to go about doing this though. Can you direct me to instructions, please?

HoosierGardener

Adding photos to existing entries in the database is really easy. Just go to the entry for the plant and scroll down to the bottom of the page. You'll see a link to "Upload a photo." Click on that and it will take you to a screen that will allow you to search for the photo on your computer.

Adding a new plant is a bit trickier, just because you need to know a bit more about the plant. If you click on the "Database" link on the left hand side of the page, that will take you to the main Database page, where you'll see a link to "Add a new plant to the database." Just follow the instructions. If you get stuck, a request for help can be made in the Plant Database Forum. http://garden.org/forums/view/...
Hope this helps!

How do we add a picture to our own profile ?

Just go to your Profile page (click on the little person-shaped icon at the top of the blue column on the left) and click on "Change your public profile." Scroll down a bit and you'll see a place to upload a new photo for your avatar. (You may need to tinker with the photo you want to get it to display the way you'd like.)