I have loaded this picture with Agave vivipara, now I found out that the two on the back are Agave americana, can I load the same picture into the entry of Agave americana, of course with a note about the central one?

For photos like this, upload it to the Multi-Plant Photo area (found under Goodies) and tag both plants with their appropriate plants. Then the image will automatically appear in the database entry for both plants, along with a snazzy box drawn around each one with a label of its name.

Thanks Dave, I'll do that!