Google’s display ads, or  ads with images, have been showing up across the Web and even in Times Square. Now they are bound for Gmail.

Google started showing the ads alongside people’s e-mail in-boxes on Jan. 21. The company is still experimenting with them and not every Gmail user will see them, said Rob Shilkin, a Google spokesman.

Ads in Gmail have always been related to e-mail messages. For instance, if Gmail users are corresponding with friends about planning a vacation to Mexico, ads for flights or hotels in Mexico might appear. The display ads will show up according to the same formula, Mr. Shilkin said.

Gmail ads struck some users as eerie when they were first introduced in 2004, but most Gmail users have grown accustomed to them. Google says that all ad placement is automatic and no human reads private e-mail messages.

Display ads are a growing business for Google as it expands beyond the simple text ads that appear next to search results and on other Web sites.

The ads contain images and sometimes audio and video and often publicize a brand, like an airline, as opposed to suggesting a specific action, like booking a flight on the spot. Google shows display ads on two million Web sites, including several of Google’s own, like YouTube, Google Finance and now, Gmail.

The ads appear next to e-mail messages that contain many images, like a promotional e-mail from a department store with photos of clothing, Mr. Shilkin said.