a simple batch resize where you can set the pics to fit in a FOR EXAMPLE:
35x65 window and an option to contraint proportions or uncheck the box to just resize it to 35x65 would be sufficient I think.
most people I know in the graphic field use it for web images, or displaying box art type stuff and want all the images to be a single size.
so I think that would be the most important way to do it.
but as in anything else, you're the author and it's your app. Just making a nice suggestion.
I personally love the app already, just looking for a feature I commonly use, that's all...