There were two Tiger Moths registered as VH-WPK, but only one Tiger Moth registered VH-WPO.
VH-WPK (1) (construction number T113) was built in Australia by De Havilland Aircraft at Bankstown, and initially registered to William P Kemp (hence the registration WPK) in Queensland on 8 October 1956. On 22 March 1960, it was re-registered VH-API, and was cancelled from the register on 30 December 1964 (reason unknown).
VH-WPK (2) (construction number 84529) was built by De Havilland in the UK and allocated the British military serial T8256. It then joined the British civil aircraft register as G-AOFG. It became VH-AWI on 8 November 1957. On 5 Oct 1960 it was re-registered as VH-WPK to William P Kemp, Corinda Heights, Qld. VH-WPK was exported to the USA in 1969, initially registered there as N5676 and then N38KH.
VH-WPO was built in Australia by De Havilland Aircraft at Bankstown, and allocated RAAF serial A17-132. On 4 July 1947, it was registered VH-AQX. Initially based in NSW, it was registered to an owner in Queensland in March 1956, but still registered as VH-AQX. On 19 January 1957 it was re-registered as VH-WPO, to the same owner as VH-WPK - William P Kemp. On 31 December 1963, it was cancelled from the register as withdrawn from use, due to a Department of Civil Aviation policy.
Based on the above information, if the photo was taken in 1956, it is likely to have been the first VH-WPK (cn T113).
regards,
David Eyre