Tool to Label Images for Supervised Classification
If you are specifically looking to outline the whales, seems like FastAnnotationTool could work:
https://github.com/christopher5106/FastAnnotationTool

Other options here:
https://en.wikipedia.org/wiki/List_of_Manual_Image_Annotation_Tools

When had to annotate many images for a project, I built a fairly simple MATLAB gui that displayed images.  I cycled through each image and if I clicked on a point on the image, that image was annotated and the point where I clicked was saved in a corresponding .mat file (.csv would have been better). It worked... mostly.  I'd guess between python and OpenCV, this could be done easily without MATLAB.