marekki

Marekkis Watermark-Plugin for WordPress can watermark your pictures an two different ways:
<ul>
<li>Insert your watermark while the picture is being uploaded.</li>
</ul>
After the activation every picture that you will upload with wordpress build-in media-uploader will be watermarked.
In the configuration-screen you can set up the position and the type of your watermark. It can be your logo (.png-file) with transparent background or a free text with color, font, size, shadow and transparency-level of your choice. See screenshots.
<ul>
<li>Insert your watermark on all chosen pictures from a directory on your web-server.</li>
</ul>
Marekkis Watermark makes possible to create a watermark on mediafiles that are already uploaded on your server. So you can mark all your old pictures with the new watermark.

Marekkis Watermark-Plugin

daxiawp

Automatically add a picture watermark, can select text or pictures are two types. 自动给图片添加水印，可选择文本或图片两种类型。 
详情：<a href="http://www.daxiawp.com/dx-watermark.html" rel="nofollow ugc">http://www.daxiawp.com/dx-watermark.html</a>
<h3>Arbitrary section 1</h3>

DX-Watermark

The pictures automatically add watermark. 图片自动添加水印.

Marekkis Watermark-Plugin vs DX-Watermark