Checkout Config: Extra Product Images« Products & Images
Checkout > Configuration > Extra Product Images
1. Gallery Content Tab
This is set to “Yes” by default. This option will display extra product images in a tab if content tabs are available.
2. Thumbnail Dimensions
This is set to 125px by 125 px (pixels). It determines the size of the additional product images in the gallery (note this is not on product pages)
3. Number of Thumbnails per Page
This is set to 3 by default. If there are more than X amount of additional images on a product then a link to the gallery is displayed to view the rest of the images.