I recently came across this great iPhone app for photographers called Marksta. It was developed by a photographer to watermark his photos on his iPhone or iPad before immediately uploading the photos to Facebook, Flickr, Instagram or some other photo sharing website.
It’s a little clunky, but once you set up your own personal template in the phone, you can apply it to all your photos before posting it. And using a template makes it easy. You can set your own font and color up and maybe save 2 different templates. One in Black and one in White, since some photos have different lighting and you’ll want to tag them quickly. There is even a nice line feature where you can set the copyright off by a hairline rule. You can position it in different locations. I really wish there was a ‘vertical’ positioning, though, so you could put it along the right margin for a vertical photo. And there doesn’t seem to be a way to size the text. There is a transparency feature, but it’s not marked well.
You can also easily upload with the built-in upload buttons for tumblr, flickr, Facebook and photo apps (all the other available options). There are also built-in buttons for easy e-mail, access to contact list and print.
If he ever upgrades it with the features I mentioned, it would make it even better.