How to differentiate between a sphere and a disc??

I have been given two images, one each for a disc and a sphere.I need to identify correctly both of them. Could anyone suggest some algorithm for the same?? Thanks in advance.

[Star Strider]

Attach the images to your Question (use the ‘Edit’ icon to open it for editing) using the ‘paperclip’ or ‘staple’ icon. It is impossible to suggest an approach without seeing the images themselves.