You can have a higher resolution image of any Flickr Photo using FlickrGetHighRez extension in FireFox that lets you view the largest available resolution of any image/photo on flickr.

How to use :

Install the Firefox Addon next right clicking on any image/photo, in flickr, and selecting the “Flickr: Load HighRez” menu item will launch a new window with the pointed photo in its largest resolution.

My Observation: I have observed that not all the latest images/photos on Flickr have an higher resolution image,But older images/photos were having higher resolution images.

Downlaod FlickrGetHigh from here.