Finite-Element Digital Image Correlation (FE-DIC) now appears highly relevant in the experimental mechanics community thanks to its direct bridge with simulation. However, using the fine FE mesh generated for accurate simulation inevitably requires the proper regularization of the inverse DIC problem. Here, Truncated Hierarchical B-Splines (THBS) are considered in a Free-Form-Deformation DIC approach to regularize FE-DIC in a strong, non-invasive, and adaptive manner. The idea is to embed the fine FE mesh in a THBS box whose unstructured refinement is automatically performed during the process to arrive at an optimal number of Degrees Of Freedom (DOF) for the solution. The FE DOF are related to the THBS DOF so that we end up with a regularized but conventional FE measured field which can be computed from a standard FE-DIC code. The method is also extended to cover stereo-DIC applications.