There are a few strategies for link to images in your newsletter. One is attribution: linking back to the source.
Here’s what happens when you don’t link:
Instagram, Twitter, Giphy, YouTube… will all link to their sources when clicked.
If you’re using an image from an article — which I do not recommend, because someone could make a rights claim against you — make sure it links back to the article and sends them traffic.
Likewise, if you’ve got an ad, the ad must link to the site of the advertiser.
If not, the advertiser won’t pay or you will have to run it again for free (known in the business as a “makegood”) because the full value was not delivered.