This is a pre-project idea to submit as part of your proposal if your plan is to add visual thumbnails for Pencil Code.
Create the start of a utility to take a picture with a webcam and do preliminary image processing as a button within Pencil Code.
Don't worry if your project seems incomplete - the purpose is to give you a chance to warm up with the code. Send a link to your fork along with your project proposal for Google Summer of Code.
Is this all that needs to be done for the whole GSoC project? Of course not - we would also need to implement storage and a full UI for tweaking and sizing and managing images. In the limit, students may want a full-featured paint program; however, something simpler would already be an awesome and acceptable GSoC project.
In the full GSoC, you may choose to propose a specific design for a complete solution.