You could mark an object on an image using either the annotation or vector tools in ENVI. For annotations, display the image and go to Overlay ->Annotations. You can draw polygons, lines, points or shapes and save the annotations to be restored at a later date. Alternately, you can create a vector layer based on the image dimensions/map information under Vector ->Create New Vector Layer ->Using Raster Image file. This also allows you to draw polygons, lines and points and also to add attributes to the vector objects. -MM