Hello! successfully able to calibrate a rather crappy papercraft spectrometer build (crappy build to great instructions:) )
I had a ton of trouble using the spectrometer on my smartphone. I was able to capture a picture of a spectrum, but got extremely frustrated with the uploading wizard. my spectrum always came in vertical regardless of whether i selected 'vertical' or not. I almost gave up but instead tried attaching the spectrometer to my laptop webcam and doing a live capture. This was way more intuitive as you see the capture line and can move it around with drag and drop functionality.
So, if you are struggling with uploading a photo and trying to rotate the image, i recommend you use a webcam instead, it is much more satisfying! If you must upload an image, realize that you have to set which row of pixels the spectrum is captured from.
Thanks for all these resources, excited to keep working through them!