<p>Substitution boxes (s-boxes) are critical components in block cipher systems. This paper proposes a novel method for constructing s-boxes based on an improved Maiorana–McFarland (MM) construction method. The technique first employs this improved MM construction to generate two distinct cryptographic functions: Bent functions and first-order resilient functions. These cryptographic functions are then used to form initial s-boxes. The initial s-boxes are combined and optimized via two auxiliary functions to produce the final s-box. The effectiveness of this approach is rigorously evaluated through key s-box metrics: bijectivity, strict avalanche criterion (SAC), nonlinearity (NL), bit independence criterion (BIC), linear approximation probability (LAP), and differential probability (DP). The resulting s-box achieves an NL of 106.50, SAC of 0.5015, average BIC-SAC of 0.4983, and average BIC-NL of 104.50, while demonstrating low LAP (0.1250) and low DP (0.0391), confirming strong resistance against linear and differential cryptanalysis attacks. Comparative analysis with other s-box designs demonstrates superior performance. The robust encryption capability is validated by encrypting standard grayscale test images (<i>Lena</i>, <i>Peppers</i>, <i>Goldhill</i>), showing significant differences in visual content, histogram distribution, and adjacent pixel correlation. Unlike conventional single cryptographic function approaches, our scheme exhibits enhanced resistance against algorithmic attacks, and this study provides significant inspiration for cryptographic function-based s-box design.</p>