Below are instructions on how to get a full width photo below your product images on your product page like this:
You can see the live demo version of this page here
To utilize the product.full-width-images template you can follow these steps:
1. From your Shopify admin, head to your Products section and select an existing product or upload a new one. Select product.full-width-images in the Template dropdown menu:
2. In the product’s Description, insert an image.
3. In the "Image alt text" field, enter any text that you wish to display over the image, followed by the alignment you wish it to have (type left, center or right in square brackets).
**IMPORTANT: Even if you don't want any text on your image, you must still include an alignment tag in the Image alt text field input area, in order for this full-width image feature to work***
The image you insert will then display full width below the main product image gallery and product description. Be aware that this full-width image style will be applied to all images that are added in this way to the description area.