I stumbled upon a new free app the other day called YouDoodle. 
There are two free versions. I chose the one that does not say plus. Plus has advertisements that were questionable for the classroom.
We used it in a similar manor to the slope project in Notability. I wanted something free that others could use if Notability wasn’t available to them.
The students were instructed to take 3 pictures, one to represent each of the following types of graphs: linear, exponential, and quadratic. They saved each YouDoodle edited image to their photo library and then used a photo collage program (whatever they had available) to combine the three. Here are some of the examples.
You may use my transparent graph for this project if you don’t have your own. The link is found here. We did have some trouble with the graph not inserting as transparent. Email me if you have the same trouble, I have a few solutions that might work for you. In You Doodle, you need to begin with your picture as a new background, then insert the transparent graph as a foreground. I found that merging the two together makes it easier to erase later. You can use the pen tool, text tool and any of the other features available. Try it out and see what you think.
Infinitely Teaching 