1. A method comprising: generating a plurality of image objects by segmenting a digital image using object-oriented image analysis; selecting selected image objects from among the plurality of image objects; displaying one of the selected image objects on a graphical user interface; determining a value of each of a subset of image features of the plurality of image objects, wherein the subset of image features constitutes a custom image-based biomarker; calculating magnitudes of the custom image-based biomarker for each of the plurality of image objects; and changing the image features included in the subset of image features such that magnitudes of the custom image-based biomarker for the selected image objects are greater than the magnitudes of the custom image-based biomarker for image objects other than the selected image objects.