"We're always trying out new ad formats and placements in Gmail, and we recently started experimenting with image ads on messages with heavy image content," a spokesperson wrote in an e-mail to Mashable. Google began running the test ads on Friday, January 21.
The news came to light when Greg Sterling, a contributing editor at Search Engine Land, shared a screenshot of a display ad that appeared in his inbox this morning:
Google has been looking for ways to expand its display ad network, and Gmail is a logical next step. Google can serve ads based on keywords that appear in a user's personal Gmail (Sterling was served an ad for organic men's tees after opening an e-mail from a clothing retailer), although those ads will no doubt be distracting for many Gmail users. Yahoo Mail already serves display ads in users' inboxes.