In order to configure Twitter Cards tags for Magento 2 product page (e.g.: product image for Twitter) please go to Admin Panel > Catalog > Products.
Once you have chosen a product you're interested in, click on it and find the Twitter Cards Metadata section.
Twitter Cards Metadata
1. Set an Twitter Cards Title. In case you haven't set it up the Meta Title will be used. If it isn't configured a category name will be used.
2. In the Twitter Cards Description set the description of the twitter card. Meta description will be used if you leave this field blank. If none of the descriptions have been configured, the Default Description will be used.
In order to set the product's Twitter Card Image (Twitter image) find Images and Videos section to add a new image or edit an existing one.
Chose the image you like and set the Twitter Cards Image Role for it.
Set the Twitter Cards Image, otherwise, Default Twitter Image will be used.
Once all of the configurations have been finished don't forget to press the Save button.