Yes, the sentence is grammatically correct. It encourages people to share their unedited selfies in a thread so that someone else can use Photoshop to edit them. The phrase "This should be fun" implies that the activity is intended to be enjoyable and lighthearted.
Here are some possible rephrasings:
1. "Feel free to share your unedited selfies in this thread, and someone will help you edit them with Photoshop. It should be a fun experience!"


