I've decided to start watermarking all my images. Not to prevent people from stealing them. A watermark may discourage stealing, but won't prevent it.
But rather so that when an image is used, the image will at least provide credit. With the rise of services such as pinterest, more and more images are being shared, and it seems that often the credit to the original photographer can get lost. So this way, my images carry with them (visibly) the credit and branding.
The type of watermark I have decided to use is not really a watermark per se. But instead I am using a border round the image with my name and website address included in the bottom of the border. There are a couple of reasons I chose to use this style of watermark.
The first is that I don't think it distracts from the image as much as a standard watermark. None of the image is covered up by a watermark at all. It also allows including more information (such as my website address) than you could include in a discreet watermark.
The second reason is purely technical. A standard style watermark that overlays the image should ideally be positioned at a different place in the image depending on the image content. The tone of the watermark will also be dependent on the image, e.g. a white watermark will show up well on a dark image, but not on a bright image.
This would make it difficult to apply watermarks to existing images without going through them manually. It would also mean extra work when uploading new images, either having to upload pre-watermarked images or specifying the tone and placement of the watermark with each image. These issues don't exist with a border based watermark, which can be the same for every image.
One disadvantage of a border watermark is that an image thief can easily crop the image from the border to get the full image with no watermark. However, cropping an image to remove a standard watermark (unless you use a strong watermark that goes straight through the middle of your image) is something image thieves often do anyway, so I don't see it as a big disadvantage.
Funnily, I seem to know more about US copyright law than UK copyright law. Mainly just because most articles online cover the US laws. I know that in the US if an image has been cropped to remove a watermark, then this can be used to prove wilful infringement, which has greater penalties for the infringer. So this in itself can be a good reason for adding a watermark to your images.
So, that's my reasons for watermarking my images, and why I've watermarked them in the style that I have. Of course, I may change my mind in the future, but I thought I might as well share my thoughts in case it helps anyone else thinking about how best to watermark their images.