Photoproduction of the Θ+ pentaquark on the proton is analyzed by using isobar and Regge models. The difference in the calculated total cross section is found to be more than two orders of magnitude for a hadronic form-factor cutoff Λ > 1 GeV. Comparable results would be obtained for 0.6 ≤ Λ ≤ 0.8 GeV. The contribution of the Θ+ photoproduction to the GDH integral is also calculated. By comparing with the current phenomenological calculation, it is found that the GDH sum rule favors the result obtained from the Regge approach and isobar model with small Λ.