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.
The idea is to familiarize yourself with the pencil code and also start working with the issues around webcam use and image processing within pencilcode's javascript.
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.