For YouTube creators, catching the eyes of potential new viewers starts with a good, custom thumbnail. It’s a skill many video-makers have honed over time, even making the effort to teach other creators what makes an appealing image: high quality images of faces, bright backgrounds, concise text. Currently, however, YouTube is testing out a feature that it hopes will improve auto-generated thumbnails — a move that has some creators on edge.

Over the next few weeks, YouTube will be running an experiment in which 0.3 percent of viewers will see auto-generated thumbnails, rather than creators’ custom-made images. “We are not removing the ability to create your custom thumbnail, but we hope to gain insights on auto-generated thumbnails for the future,” the company clarified last night. Another rep on Google’s product forums pointed out that good auto-generated thumbnails is “a top request we get from creators who use them.” The feature may be temporary, but online, creators are already voicing serious concerns. Many say they’re frustrated with the lack of transparency about the experiment; others point out how much time they put into their thumbnail images, or even the money they spend paying others to do the same.

“You shouldn’t just.... run experiments on us without our consent?? at least let creators opt-in to this if they want,” wrote Riley J. Dennis on Twitter. “[B]ut there’s a reason we design our own thumbnails. [Y]ou’re harming our branding and engagement for your own research purposes.” Another creator, Chilled Chaos, pointed to a lack of communication about which creators are impacted. “People pay others to create these, why ruin that? And .3% isn’t small when you’re talking about 1.5 billion monthly users,” the YouTuber said. “This job is extremely volatile and we watch numbers like Hawks. We already have to cater to an ever-changing market, can we not have an ever-changing platform without you keeping us in the loop?”

YouTube frequently experiments with different features or changes on its platform, and for now it says it has “no current plans to change or remove the ability to add custom thumbnails.” The company’s interest in automated images is understandable, given both its obligations to advertisers and problems with bad actors abusing its algorithms. Furthermore, it aims to help users who are interested in auto-generated images, rather than making their own.

But creators’ concerns that YouTube’s experiments — even if well-meaning — could hurt their potential revenue isn’t unfounded. As Motherboard once explained, “thumbnails play the internet-equivalent role of a movie poster, enticing you to click and watch.” Automatically generated images aren’t always going to be representative of what that video has to say, let alone be compelling enough to click on. As creator Ricky Dillon put it on Twitter: “Sometimes you get so unlucky and your auto generated thumbnail is something random like a tree or a FOOT.”