This book constitutes the refereed proceedings of the 4th International Joint Conference on Discrete Geometry and Mathematical Morphology, DGMM 2025, held in Groningen, The Netherlands, during November 3-6, 2025.

The 37 full papers included in this book were carefully reviewed and selected from 52 submissions. They were organized in topical sections as follows: Discrete Geometry - Models, Transforms, and Visualization; Computational Aspects of Discrete Structures and Tilings; Discrete and Combinatorial Topology; Hierarchical and Graph-Based Models, Analysis and Segmentation; Algorithms; Morphological Filters, PDEs and Multivariate Morphology; Mathematical Morphology and Digital Geometry for Applications.