Half the fun of surfing the Internet is stumbling across tasty little Web treats that you never would have thought to look for.

Traditional social bookmarking sites like Digg and Delicious are great for finding articles and other text that other Web surfers have tagged as interesting.

For the visually oriented, the pickings have been slim. Now, however, a handful of photo-oriented bookmarking sites are emerging to entertain the eye as well as the mind.

The sites — We Heart It, FFFFound and Vi.sualize.us — resemble constantly changing art installations. Similar to a white-walled gallery, they present their goods with little to no flourish: simple, clean interfaces are all that stand between visitors and eyefuls of color.

The sites work similarly to their text-based brethren. When members discover an image worth preserving, they bookmark it, either by right-clicking or using a site-specific browser button. Although the sites are still light years away from the popularity of their older siblings -– Digg alone boasts 35 million unique users per month and as many as 20,000 submissions per day -– they are steadily gaining a loyal following.

Here’s a bit more about each of the sites. Please note that images on all of them can be slightly not-safe-for-work, so proceed with caution when browsing.

FFFFound: Tokyo-based design firm Tha started FFFFound as a side project in June 2007. “We just genuinely wanted to share images that are considered good by a community of people,” said Erica Sakai, a spokesperson for the company. “At the time, there were no Web sites that offered this kind of service.”

As members add fresh fodder to the site, images appear and drift down the homepage, forming a steady stream of album covers, typographical posters, experimental photography and snapshots of street graffiti.

Unlike the other sites, FFFFound is a closed to new contributors. Ms. Sakai said the team elected to cap the community’s size for fear FFFFound would become overly cluttered and unmanageable. But any visitor is free to browse the catalog of 500,000 images.

Vi.sualize.us: Victor Espigares, a software engineer in Spain, was flipping through a photographer’s portfolio on the Web when he was struck by a particular image. “I was thinking about bookmarking the picture — but not the site — and found that I had no choice,” said Mr. Espigares. “So I started to think about filling that need. Later, I started to think a little bigger and realized that others might have a similar need.”

Vi.sualize.us features more variety than the other sites: anything from T-shirt designs to artsy studio shots and illustrations are likely to pop up. Since the site began in September 2007, the community has expanded to roughly 10,000 members with a collection of nearly 300,000 images.

We Heart It: Unable to land an invitation to FFFFound, Fabio Giolito, a Brazilian Web developer, created We Heart It in March partially as an alternative to the exclusive site.

“As a designer, I keep an inspiration folder on my computer where I throw all the cool images and links I find,” said Mr.Giolito. “I created the site to organize things that I like. People liked it, so I opened it to everyone.”

With its wealth of portrait and fashion photography, the site is similar to Flickr but with a more risqué and avant-garde feel. Unlike the other two visual-bookmarking sites, We Heart It also allows its 16,000 registered users to tag favorite videos from Vimeo and YouTube. The site currently has more than 200,000 submissions, and Mr. Giolito estimates a new selection is added each minute.

Which photo-tagging sites did we leave out? Let us know your favorites in the comments below.