There are a few ways to add a border around an image in Illustrator.
You can use the Stroke tool to create a border around the image. First, select the image. Then, click on the Stroke tool in the toolbar. In the Stroke panel, choose a color for the border and an appropriate width. Finally, click on the "Stroke" button at the bottom of the panel.
Another way to create a border is to use the "Frame" tool. First, select the image. Then, click on the "Frame" tool in the toolbar. Click and drag around the image to create a frame. In the frame options, you can choose a color and width for the border.
You can also add a border by creating a new layer. First, create a new layer. Then, select the image on the layer below. Click on the " Stroke" tool in the toolbar. In the Stroke panel, choose a color for the border and an appropriate width. Finally, click on the "Stroke" button at the bottom of the panel.
