AI Thumbnail Generator: Make Video Covers That Actually Get Clicked
A thumbnail has one job and about half a second to do it. What decides it is contrast, a single clear subject and text short enough to read at 168 pixels wide.
Most underperforming videos do not have a content problem, they have a packaging problem. The thumbnail and title decide whether the video gets a chance, and the thumbnail is doing its work at a size where almost nothing survives — a phone in a feed shows it smaller than a postage stamp.
OpenFilmo generates thumbnail candidates from your stills or a description at 2 credits each, so producing enough variants to actually test is cheap. The composition is generated; the words are added afterwards, because short text inside a generated frame is the least reliable part of any image model.
What it does
Built for this specific job, not a generic generator.
Variants worth testing
Generate several compositions from one source so you are choosing between options rather than defending one.
High-contrast composition
Built for readability at feed size: one clear subject, strong separation from the background, no clutter.
Sized per placement
Export 16:9 for YouTube, 9:16 for Shorts covers and 1:1 where a square crop is needed.
Consistent channel look
Reuse one style description so a channel reads as one brand instead of a row of unrelated images.
How it works
Four steps, no timeline to learn.
Start from a still or a description
A frame from the video works well, because the thumbnail should promise what the video delivers.
Generate several candidates
Produce three to five variants. The point is to have something to choose between — one option is not a test.
Add the text yourself
Keep it under four words and add it in your editor. Generated text at thumbnail size is unreliable and costs retries.
Check it at actual size
View it at 168px wide on a phone before publishing. If the subject is not obvious at that size, it will not be obvious anywhere.
What people make with it
The jobs this actually gets used for.
YouTube video covers
A 16:9 cover with one subject and a short phrase, consistent across a series.
Shorts and Reels covers
9:16 covers sized for the vertical shelf.
A/B testing
Two or three variants per upload, rotated to find which composition earns the click.
Playlist and series art
One style reused across a playlist so a series is recognisable in a grid.
Why thumbnails fail at small sizes
Everything that looks good in the editor is being judged at a tenth of that size.
The most common thumbnail mistake is designing for the canvas instead of for the feed. Detail, secondary subjects and long captions all read fine at full width and disappear completely at the size a viewer actually sees.
The second mistake is trusting generated text. Short words at small resolution are exactly the failure case for image models, and a misspelled or garbled word on a cover is worse than no word at all. Generate the composition, then set the type yourself.
Testing is where the leverage is. Generating five variants costs 10 credits; the difference in click-through between a good and a mediocre cover on the same video is often larger than any change you could make to the video itself.
Credits and plans
Generation is metered in credits, shared across every tool.
One image costs 2 credits and a 4K upscale costs 4. The Free plan gives you 30 credits every month with no credit card, no watermark and commercial use included. Paid plans start at $9 for 400 credits and add faster generation and parallel tasks.
Related guides
Longer reads on the same workflow, from the OpenFilmo blog.
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AI tools
Single-purpose tools that run in the same workspace, on the same credit balance.
Vidu models
The Vidu Q1 and Q2 models this site runs on, and how they compare to Kling, Veo and Runway.
Related workflows
Closely related tools and guides on the same problem.
Frequently asked questions
What size should a YouTube thumbnail be?
16:9, and the common working size is 1280x720. Judge the design at roughly 168px wide, which is closer to how it appears in a feed on a phone.
Can the AI write the text on the thumbnail?
It should not. Short generated text at small sizes is unreliable. Generate the composition and add the words in your editor, keeping them under four words.
How many variants should I make?
Three to five per video. At 2 credits each that is 6 to 10 credits, and the point is to have options to choose between rather than one defended design.
How much does a thumbnail cost?
One image costs 2 credits. The Free plan gives 30 credits per month with no credit card. Paid plans start at $9 for 400 credits.
Can I keep a consistent look across my channel?
Yes. Reuse the same style description every time so covers read as one brand. Without a fixed style prompt, output drifts between uploads.
Do the thumbnails have a watermark?
No. Exports are watermark-free on every plan including Free, and commercial use is included.
Can I use a frame from my video?
Yes, and it is usually the best starting point, because the cover should promise what the video actually delivers.
Should I test different thumbnails?
Yes. Rotating two or three covers on the same video is a cheap test, and the click-through difference between variants is often larger than most changes to the video itself.
What makes a thumbnail get clicks?
One clear subject, strong contrast against the background, and text short enough to read at feed size. Clutter is the most common reason a cover fails.
Video prompt collections
Copy-ready prompt sets for text-to-video, image-to-video, product, UGC, social and tutorial clips.