MATLAB can't do this directly. You'd need to use ActiveX programming to call Excel API functions. Fortunately MATLAB can do that (make ActiveX calls). I don't recall doing that (stuffing images into Excel) so I don't have any demo code for you.
It's going to looksomewhat similar to this:
% Open Excel file.
objExcel = actxserver('Excel.Application');
objExcel.Workbooks.Open(fullfile(excelFilePath, excelFileName)); % Full path is necessary!
oWB = objExcel.Workbooks.Add();
oSheet = oWB.ActiveSheet;
oSheet.Pictures.Insert("<< full path to image file >>").Select();
But you can look up ActiveX in Answers or elsewhere. Here's one example: