How to find an irregular shape

Hello,

I am working on a project where i am to classify objects. I am doing this classification based on their colour and shape in the first two tiers. I've made an algorithm that works just fine for the colour by simply checking what colour the image is mainly made up of. After that i want to find the shape of the image.

I've looked at basically all of the tutorials and guides on this forum and have not found anything that works for me, and i'm kind of out of ideas. The main problem is that there are thousand of images of the objects, where the distance, angle and lighting differs. The masking that most people have suggested here doesn't work for me, neither does the corner detection due to the low amount of pixels in the images.

So, to clarify the question, how could i get started on an algorithm that find the shapes of images of this quality:

Since the quality is so low i cant find anything useful basically.