Dimensions used to display images in publishing sites are referred to as image renditions.
Details
Image rendition is currently not maintained when migrating from a SharePoint 2013 source and up.
This means that if you migrate an image from your source environment after modifying the defined image rendition, the image will copy but the image rendition will not be updated to match that at the source.
Workaround
There is no workaround at this time.