Google is joining a $5.75 million investment round in Pixazza, a start-up that hopes to profit by overlaying photos on the Web with links that let people buy the products in the images.

The Mountain View, Calif.-based company is now launching the technology for general use by advertisers, Web publishers, and the network of self-appointed but screened specialists who identify the products in the photos, said Chief Executive Bob Lisbonne. The company is starting with the apparel industry but plans to expand to home design and furnishings, travel, electronics, and sports starting later this year, he said.

Lisbonne likens Pixazza's technology to a photo-based version of Google's AdSense, which analyzes text on publishers' Web sites and displays what it deems to be relevant ads. AdSense is used widely by publishers to generate income from their Web sites without having to hire an advertising sales force.