The volume set LNCS 15621-15622 constitutes the refereed proceedings of the 21st International Conference on Computer Analysis of Images and Patterns, CAIP 2025, which took place in Las Palmas de Gran Canaria, Spain, during September 22-25, 2025. The 65 full papers were carefully reviewed and selected from 109 submissions. The proceedings focus on Facial and Video Recognition, Image Segmentation, Object Detection and Applications, 3D Vision and Reconstruction, Biomedical Imaging and Diagnostics, Model Robustness and Generalization, Multimodal and Vision-Language Models, Robotics, Interaction and Intelligent Systems, Emerging Methods and Vision Applications.