Please make sure about certain criterias listed below, in order to have guest pitcure / images visible on all the machines.   


1)  All the machine should be connected in same network

2)  The folder, that you have selected to save guest images is SHARED with all the client.


Refer the screenshot below. 

1)  Where to select desired "Folder" path.


 


2) Share "Folder" with all the machines connected with same network.