By default Windows doesn't recognise file systems formatted using Linux ext, however, Images containing Linux ext file systems can be browsed by using a free Windows driver. 

Download Ext2Fsd  from here:  https://sourceforge.net/projects/ext2fsd/

Once downloaded, run the installer accepting any defaults. 

De-select launching the volume manage as this isn't required. 

Linux ext partitions in Macrium Reflect image files can now be mounted and explored.

See also: Linux ext file systems used and total space in Reflect