Looking for a plugin that re-sizes images without re-sizing the image.

Ok let me explain. Lets say on my home page I want to but a blog images that’s 600 width X 1000 height. But all that height on my homepage will look bad but I would like people to see the full image when they click my blog title. My question is is their any plugin that lets me crop or only show the top half of the image or a selection of the image that could be 600 width but 300 in height. Then under that I typically will have 2 paragraphs then a “read more” link. But in the actual post it shows the full size with the paragraphs at the end of the larger pic. Hopefully I explained myself well since I had no clue what to type into google to find this. Thanks in advance.