Notability for the iPad has a pretty powerful photo/image editor that can be useful when you are putting annotated images in your notes.
First, you want to add a photo to a note by going to the plus icon in the upper right corner of a note screen. Once you have your image in the note, touch and select the image and make the following menu appear above the image. Select Edit from that menu.
There are a couple of tools you can use. Select the drawing tools icon to select objects, freehand draw, place shapes, and write text.
The color toolbox allows you to change the fill and outline (stroke) of your objects. The Alpha slider makes an object more or less transparent. This is a good group of tools to use if you want to place a transparent object, like a green tinted circle, around something important in your image.
When you are done, press the done key in the upper right and your image, with all the annotations attached to it will go into your note. The benefit is that the annotations will stay with the image even if you move it around. And, you can go back and change the annotations in the photo editor tool if you want to make changes.