You can already train an image model for hand gestures. Today in Scratch you will load that model into a rock, paper, scissors game and play against the computer.

Before you build, think: what might go wrong if the model is only slightly sure about a gesture? Have your model's link ready: you will start a new project and build the game step by step, testing it as you go.

Your rock, paper, scissors game has four parts:

1. Load your model into Scratch so the project can use it.
2. Read what it sees from the webcam, and only act when it is confident enough.
3. Pick the computer's choice at random.
4. Compare the two and decide win, lose or draw.

The confidence threshold is the interesting one: it decides how sure the model has to be before your game acts on what it thinks it sees.

Set up a new project in Stretch3 with the TM2Scratch extension:

1. Go to https://stretch3.github.io/ and start a new project.
2. Delete the Cat sprite.
3. Click the Extensions button at the bottom left of the screen and choose TM2Scratch (not TMPose2Scratch or Posenet2Scratch). This extension lets you use Google Teachable Machine image models in Scratch.
4. The extension tries to use your computer's camera straight away. If your browser asks, click Allow. You should now see what the camera shows on the stage.

Scratch: How to add extension blocks

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Understanding and Adding Extensions in Scratch

What are Scratch Extensions?

Scratch Extensions are additional sets of blocks that expand the capabilities of your Scratch projects. They allow you to:

1. Mention extensions like Pen here
2. Connect with external hardware (e.g., microbits)
3. Access web-based services (e.g., Google Translate, Amazon Text to Speech)
4. Use more advanced programming features

How Extensions Work

When you add an extension to your project:

• New blocks appear in the blocks palette
• These blocks are grouped under a category named after the extension
• You can use these blocks just like any other Scratch blocks

Adding an Extension to Your Project

1. Look for the "Add Extension" button in the bottom-left corner of the Scratch editor
2. Click the "Add Extension" button
3. A window will open showing all available extensions
4. Browse through the options or use the search bar to find a specific extension
5. Click on the extension you want to add
6. The extension is now added to your project, and its blocks appear in the blocks palette

Add a new sprite to the project that will represent the computer's choice in the game. You can choose any sprite you like, but for this example, we'll use the 'Gobo' sprite.

Scratch: How to add a sprite from the library

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To add a sprite from the sprite library follow these steps:

1. Put your mouse over the Choose a Sprite button
2. Click on the magnifying glass
3. Find the sprite you want in the library
4. Click on your chosen sprite

You can use search box or the filter links (Animals, People, Fantasy etc) to locate your sprite.