1. A method comprising: identifying a plurality of users of an online system participating in a video conversation, each user having a client device presenting visual representations of one or more users of the plurality of users; receiving user information describing actions performed by the plurality of users on the online system; determining a geographical location visited by each of the plurality of users based at least in part on the user information; in response to receiving a selection from one of the plurality of users for a background graphic for the video conversation, for each user of the plurality of users: providing the background graphic to be included in a composite view presented by the corresponding client device of the user, the composite view overlaying the visual representations of the one or more users of the plurality of users on the background graphic, wherein at least one of a set of candidate background graphics is determined based on the geographical location; determining, for a first user of the plurality of users, a first plurality of graphics each associated with one or more designated portions of the composite view presented by the client device of the first user, the first plurality of graphics different than the background graphic and the visual representations of the one or more users; determining an impression opportunity for a designated portion of the one or more designated portions of the composite view; providing one or more graphics of the first plurality of graphics to be included in the composite view presented by the client device of the first user; and in response to receiving an interaction performed by the first user with a graphic of the one or more graphics, modifying the composite view presented by the client device of the first user by overlaying the graphic on the one or more designated portions of the composite view corresponding to the graphic.