Flame front identification typically relies on chemiluminescence or planar laser-induced fluorescence (PLIF) diagnostics. Yet, existing approaches are often limited by line-of-sight integration, low signal-to-noise ratio, or limited applicability to hydrogen flames. This study introduces a novel OH PLIF-based method that isolates the flame front by subtracting fluorescence signals obtained from two excitation lines with distinct temperature dependencies. The method is validated using LIFSIM coupled with 1D freely propagating flame simulations and is experimentally demonstrated in a laminar premixed H2[jls-end-space/]-air Bunsen flame. The resulting flame front marker exhibits a well-defined peak located, on average, 0.56 flame thicknesses from the heat release rate (HRR) peak and an average width of 1.57 times the HRR width. These values are comparable to those obtained from OH∗ chemiluminescence and the OH PLIF gradient, while offering substantially higher SNR and providing spatial resolution. Beyond introducing a new flame-front marker, suitable for hydrogen flames, this work provides a numerical and experimental assessment of OH-based HRR markers, evaluating their performance for hydrogen flame diagnostics. ... Read more