Which girl group started the photocard trend?

Girls’ Generation started the modern K-pop photocard trend with the Korean release of their 2010 album Oh!.

Photocards are small collectible idol photographs inserted into physical albums, usually with different members distributed randomly. This encourages fans to buy, trade and collect multiple copies. Girls’ Generation’s Oh! is widely credited with making the practice a major feature of Korean idol albums and turning photocards into a standard part of the K-pop retail experience.

There is an important technical distinction behind the trivia answer. TVXQ had included photocards earlier, in a 2007 Japanese release, so Girls’ Generation was not necessarily the first K-pop act ever to use the format. However, Girls’ Generation was the prominent girl group associated with bringing photocards into Korean album releases and popularizing the trend across the industry.

The group, also known as SNSD, was one of SM Entertainment’s most influential second-generation acts. Their success helped make album inclusions, member-specific collecting and photocard trading central parts of modern K-pop fandom.