This depends on your purpose. For example, if you want to post this photo on the web, then you will need a resolution of around 640x480 which would provide a decent nice and clear pic. But suppose you want more details, then a resolution of 1600 x 1200 to 2048 x 1536 should cover most purposes.
Of course, if you wish to make large prints like 8inch by 10inch, you should consider going for a resolution of 3072 or 2048 or even higher. Higher resolution is also important if you plan to crop out part of the image and then print the cropped part.