I have been grappling with this issue the past few days. I am a beginner C++/OpenCV developer trying to write a small program to learn Aruco codes. I keep getting the assertion failure (OpenCV(4.8.1) Error: Assertion failed (mtype == type0 || (CV_MAT_CN(mtype) == CV_MAT_CN(type0) && ((1 << type0) & fixedDepthMask) != 0)) in create, file /home/ci/opencv/modules/core/src/matrix_wrap.cpp, line 1393) in both OpenCV 4.8.1 and 4.10.0-dev when I try to detect a Aruco marker. This is the command used to build OpenCV for both versions: