Go out and shoot some photos that fit the theme. The projects are
supposed to encourage you to work on your photography, not just upload
an old image. To that end, you won't be able to submit any image that
was uploaded before the project was created.
Upload your new image to your Photo.net gallery.
Go to the image page and click on the "Photo Admins" tab at the bottom
right.
Click on "Submit to current monthly project".
Make sure that your image fits the theme of the current
month. Users who upload images not fitting the theme will have them
removed. Users who regularly upload images not fitting the theme will
be blocked from uploading to the monthly project.
Once your are sure that you have the image you want to upload,
click on "Yes, I wish to submit this photo".
Go visit the gallery page for the current project and see what
others have uploaded.
Enjoy feeling of having done something cool this month.
