Google just announced today how they've improved spam filtering using TensorFlow.
What's TensorFlow, you might ask? "An open-source machine learning (ML) framework developed at Google. These new protections complement existing ML and rules-based protections, and they’ve successfully improved our detection capabilities. With TensorFlow, we are now blocking around 100 million additional spam messages every day."
That's a lot of newly blocked email messages. Does it affect you, dear sender? Hopefully not, because Google says that they're "now blocking spam categories that used to be very hard to detect," including "image-based messages, emails with hidden embedded content, and messages from newly created domains that try to hide a low volume of spammy messages within legitimate traffic."
This doesn't mean suddenly it is unsafe to send image-heavy emails to your Gmail subscriber base. Google's not about to intentionally start blocking legitimate mail that people actually signed up for. But it does highlight that the closer you get to the edge of best practices -- if you have any practice failings in different areas, you could end up overlapping with one or more of these categories. If so, your messages might actually merit blocking. I'm guessing the chances that it affects a "legitimate" sender are pretty slim, though. But, just a reminder -- "Don't be like Goofus," as the old Goofus and Gallant stores in Highlights for Children used to tell us.
Spammers often do things like rotate through newly purchased domains, embed content in unique ways to try to evade filters, and use images to hide messaging from machine filter review. Don't do these things, and I think you'll probably be just fine.