To hide a Featured Image using jQuery, click this link to go to my GitHub account. Once there, click Download ZIP (on the right.) A ZIP file will download to your computer.
In your WordPress account, go to Plugins. Choose Add New. Instead of searching for a plugin, click Upload Plugin (near the top of the Add Plugins page.) Click Choose File. Navigate to and select the ZIP file you just downloaded from GitHub (hide-featured-image-jjloomis.zip.) Click Open. Then click Install Now. Then click Activate Plugin.
You will now be able to hide Featured Images on individual posts and portfolio projects. Just find the Show or Hide Featured Image box in the right panel of any post of portfolio project screen. (Remember: you will need to click Update after selecting Hide Featured Image.)