With the Substack post editor, there's a variety of things you can do with an image that's been added to a post.
Need to change the size of an image?
Once you add an image, click on the diagonal arrows at the bottom right corner of the image. This will size the image making it larger or smaller– whatever your preference.
To make your image full width, click on on the three dots in the top right corner and select "Toggle full width".
Need to add alt text to an image?
Click on the three dots in the top right corner of the image and select "Edit alt text".
Enter your text and click "OK".
Need to add a caption to an image?
Click on the three dots in the top right corner of the image and select "Edit caption".
The caption will appear at the bottom of the image for you to edit.
Need to add a link to an image?
Once you add an image and see a blue border around it, click on the Link icon in the toolbar or use the hot-key combo (command+K on Apple devices).
Enter the URL in the pop-up box and select "Link".