You can't directly stroke a linked image in Adobe Illustrator. Linked images are treated as separate objects, and Illustrator's stroke functionality only applies to vector objects.
Here's how to achieve a similar effect:
- Create a copy: Duplicate the linked image by dragging it while holding down the Alt key.
- Convert to vector: Right-click the copied image and select "Create Outline." This will convert the image to a vector object.
- Apply a stroke: Select the converted image and use the Stroke panel to apply a stroke of your desired color, width, and style.
Alternatively, you can:
- Apply a stroke to a shape: Create a shape (e.g., rectangle) over your linked image, and apply a stroke to the shape instead.
- Use a clipping mask: Create a shape that covers the area you want to stroke, apply a stroke to the shape, and then use the shape as a clipping mask for the linked image.
Remember, these methods will create a stroke effect around the image, but the image itself will remain unchanged.