Pick any standard* theme from Farktography’s history. All three of your photos must illustrate that theme.
*by this I mean themes that utilize the usual Farktography submission rules (cats, colors, vacations, etc) and exclude the specialty themes like Software Hootenanny, Panoramas, the anniversary themes, HDR, etc.
There is a (probably not updated recently) list of prior themes on the forums and that magnificent bastard who runs Bibliostats seems to have an exhaustive list of themes. So knock yourselves out!