Two weeks after Julia uploaded her wardrobe photos to a popular cloud service, her social media feeds were filled with ads for vintage jackets and limited-edition sneakers. She scrolled through her phone at lunch. "Hey, that's the jacket from my photo," she said to her friend, raising an eyebrow. Her friend looked over, shrugged, and said, "Yeah, that's how it works now. The apps always know what you want."

Lately, more people are noticing that their online choices seem less private. Companies promise to keep data safe, but stories often surface about how user information is shared across platforms. Many fashion and shopping sites use special software to analyze images, helping them match ads to your style. Shoppers in large cities, especially, are reporting that the products they see online appear closer to what's in their homes and closets.

As this trend gets stronger, questions keep popping up. Is convenience worth giving up privacy? Tech companies develop new ways to personalize, and users have to choose again and again—share a bit more for better deals, or hold back and see only general ads. One evening, Julia sat at her desk, her mouse hovering over the settings button. Her screen reflected the glow of a bright red "Personalize Ads" toggle.