In order to overlay your image on a live video feed, as video can be considered as a collection of images which are essentially matrices in MATLAB, hence adding the image to be overlayed as pixels to the collections along with appropriate alpha adjustment. A working example can be found in the below MATLAB Answer where an image was overlayed over another image:
Also, functions like 'preview' can be used to achieve the same with live cam feed. The below MATLAB Answer explains how the same can be done:
Please refer to the following MathWorks documentations for more information:
Thanks.