Mimimum size / Blank featured images

Hello, We've looked through the settings list and have not been able to find where to specify the width/height limit for retrieving images. We're currently experiencing a lot of small images getting expanded to featured image size, thus getting many pixelated images, making the feed look quite bad. In some cases the images appear in the post settings under the custom field echo_feature_image but does not display in the post itself. Where would we find these settings or how do we go about fixing this? Here is a video clip describing the issues... hope it helps: https://www.screencast.com/t/Q7pOgrcg Thanks