It is preferrably a good idea to use the same photographs but within required dimensions. The dimemsions for photograph for passport size and post card are different. So the same photo but with different dimensions can be used. According to the Information bulletin, the dimensions need to be as follows:

latest Passport size Photograph (size: 10 kb to 200 kb)

Post Card size photograph (4”X6”) (Size: 50 kb - 300 kb