Not just partnered accounts. My YouTube account lets me upload custom thumbnails, and I'm certainly not followed. I have maybe a couple dozen videos with maybe a few hundred views among them all.

Is this definitely not algorithmic? I've been noticing for a while that videos might have an incidental flash of cleavage and then that is used as the thumbnail. I'd always wondered if this was arising "naturally" somehow (people pausing that scene perhaps?)

On the basis of the type if video I'd discounted manual intervention. Though if people can just upload any image I'm now surprised that they're not all like this.

> After uploading, YT gives you 3-5 thumbnails you can choose from.

Can you pick an arbitrary video frame, or only one of the suggested thumbnails?

It automatically captures 3 different thumbnails (I guess using the algorithm in OP) and lets you select any 1 of those 3.

I presume they use the image selection as training data too—if not that seems like awfully low hanging data fruit.

Many videos seem to have completely arbitrary thumbnails which are not from the video. Most of the Epic Rap Battles videos, for example.

Perhaps this option 'unlocks' after you reach a certain subscriber count.

As mentioned upthread:

> partnered accounts are allowed to upload custom thumbnails (which can be any image, not necessarily even a screenshot from the video).