how to identify an object in the image and how to stitch two images

Hai! I have two different images of a huge device. I need to overlap these images.I came up with an idea but doesn't know how efficient it is.My idea is to identify a common object in all these images and overlap them.For example say i have upper part of the device as one image and the middle part as another image,i found a symbol on these images.Is my approach correct?Please do suggest me how to implement this.