Today we are making the /image/resize robot's zoom parameter public. Up until now it was an undocumented parameter called "dont_zoom" with a default value of "false" that only few knew about. We decided it makes more sense to make it public now so everyone can profit. It is now called "zoom" and has a default value of "true" - so everybody who used it so far, please change your Templates accordingly.
The parameter contains very useful behavior, in that it leaves images that are smaller than your specified width and height untouched when resizing them. Imagine you use the pad strategy for example with a width and height setting of 100 pixels and with zoom: false. Now if one of your users uploads a 50x50 image, the image would get centered both vertically and horizontally and have a 25 pixels black border (or whatever background you specified) on each side.
Please check out the full documentation and let us know if you like this.