automatic resizing images

when I create a poll I would like to add an image...which I already can do (via "add media"). But the problem I have is that the I think the images have to be a certain size to import (I think this setting comes from somewhere in joomla), but if I resize the image to make it small enough to be added, then the problem is that the image is very small once the poll has been created. I ask this because I want some of my polls to be of images and users voting on images. So is there a resize attribute or can you tell me how to get this working correctly without me having to resize the image before uploading.