GFXMark Free is a comprehensive tool for applying a range of watermarks to your chosen images.

The free build has significant restrictions. It works with a maximum of 10 images per operation; it has a maximum export resolution of 1200 x 800; it's for personal use only.

What you do get are a good set of watermark types, including text, images and diagonal lines.

You're able to choose your preferred font, colour, opacity, watermark position, diagonal line style, use single or tiled watermarks, and optionally add EXIF copyright tags to JPEG and TIFF files.

There's even a "brightness aware" feature, where GFXMark can adjust its colour and opacity for maximum visibility (text will be dark on a light background, or light when it's dark).