Can we use the same picture across multiple chapters of a thesis? I am writing my thesis. In second chapter, I would like to propose a model with a figure. In third chapter, I want to propose a framework which is based on that model. It would be easy for a user to understand the framework if I can have the same figure in chapter three. Is this OK to copy the same figure? Or should I just add reference to the figure in second chapter?
The reason why we have figure numbers (or for that matter, equation numbers) is to ensure that calling these numbered objects becomes easier, you can identify these things with their labels. In fact, if you keep pasting the figure over and over again, whenever it is needed in the text, you will unnecessarily lengthen your thesis, and confuse the reader, who will scroll back to the earlier instance to see what is the difference from what he/she saw there. 

Simply identify it by the figure number, and refer to it as Fig. 1.1 (or whatever it is, more generically, 


  Fig. \ref{figure_label} 


if you are using LaTeX), in all later instances when you feel the need to call it. This befits clarity, conciseness and convention - all three of them.