Lots of ways:
- There are many stand-alone packages, several of which are free, which will take the images in a folder, create thumbnails and HTML for you to put on your site. There are so many, the best way to find one that suits you is to do a search with your favorite search engine and try a few out.
- Most current big-name image-editing software can create thumbnails and code for a gallery. A free package that many people use for this is IrfanView.
- If your site has PHP you may want to try a free script package: Gallery, Coppermine, or DAlbum. The first two offer a good degree of customization, and the last has a distinct, simple interface.
- It is also possible to use a Blog engine, such as Movable Type to create a photoblog.
A good idea is to look at example or two from all of these, try them out if there is a free version, and decide which one(s) meets your needs.
Update:Suttonian
found this very complete list of free software:
Web Photo Galleries