YouTube Thumbnail Generation via Gemini

Overview

Generate custom YouTube thumbnails using Google Gemini's image generation (Pro mode). Each thumbnail is a 1280x720 image with bold text overlays, thematic visuals, and branding.

Step-by-Step Workflow

1. Gather Video Info

For each video that needs a thumbnail, collect:

• Title (already set on YouTube)
• Content type: "AI in Action" weekly jam or "Paper Club" reading
• Topic summary: What was presented/demoed (from frame extraction or title)
• Presenter name (optional, for subtitle text)
• Date in D Mon YYYY format

2. Navigate to Gemini

• Go to gemini.google.com
• Click Tools button (bottom toolbar)
• Enable Create images
• Click the model dropdown (shows "Fast" by default) and select Pro
• Confirm "Image" chip and "Pro" label appear in the chat input area

3. Craft the Thumbnail Prompt

Use this prompt template, customized per video:

Create a YouTube thumbnail (1280x720) for a video titled "[FULL TITLE]".
[1-2 sentences describing what the video is about — the demo, paper, or topic].
The visual should be [THEME DESCRIPTION]: [specific visual elements relevant to the topic].
Bold text overlay: "[MAIN TITLE]" prominently, with smaller text "[SUBTITLE]" below it.
Include a bottom bar with "[SERIES NAME] [D MON YYYY]" in bold.
Please include the Latent Space podcast logo in a corner — search the web for "Latent Space podcast logo" to find it.
Use [COLOR PALETTE] with a dark [THEME] background.

Prompt Customization by Content Type

AI in Action (demos/presentations):

• Bottom bar text: AI IN ACTION [D MON YYYY]
• Visual theme: Match the demo topic (space, gaming, dev tools, etc.)
• Colors: Vibrant, exciting — neon blues, greens, purples, electric tones

Paper Club (paper readings):

• Bottom bar text: PAPER CLUB [D MON YYYY]
• Visual theme: Academic but engaging — neural networks, brain visualizations, formulas
• Colors: Deep blue, orange, white — scholarly but modern
• Main text: Paper acronym or short name (e.g., "SDPO")
• Subtitle: Full paper name

Key Prompt Tips

• Always ask Gemini to search the web for relevant logos and reference images
• Specify 1280x720 dimensions explicitly
• Request bold, large text for the main title — readable at thumbnail size
• Include a colored bottom bar with the series name and date
• Keep the background dark so text pops

4. Generate and Save

• Submit the prompt and wait ~30-45 seconds for Pro mode generation
• Click the generated image to expand it
• Click Save to download to ~/Downloads
• Generated files will be named Gemini_Generated_Image_[hash].jpeg

5. Compress to Under 2MB

YouTube requires thumbnails under 2MB. Gemini Pro images are typically 3-4MB.

convert "Gemini_Generated_Image_[hash].jpeg" -resize 1280x720 -quality 85 thumb_[label].jpg

Naming convention: thumb_[abbreviated_date].jpg (e.g., thumb_jan31.jpg, thumb_feb7.jpg)

6. Upload Thumbnails to YouTube Studio

For each video:

1. Go to YouTube Studio → Content → click on the video
2. Click the pencil/edit icon (Details tab) in the left sidebar
3. Scroll to the Thumbnail section
4. Click the Upload file button (may be hidden — use find tool to locate ref)
5. Select the correct thumb_[date].jpg file
6. Verify the thumbnail appears in the preview
7. Click Save at the top right

File picker automation (macOS): After clicking Upload file, use osascript to navigate the native file dialog:

tell application "System Events"
    delay 1
    keystroke "g" using {command down, shift down}
    delay 1
    keystroke "/path/to/thumb_[date].jpg"
    delay 0.5
    keystroke return
    delay 1
    keystroke return
end tell

7. Verify

Take a screenshot of each video's details page to confirm the custom thumbnail is set.

File Size Reference

• Gemini Pro raw output: ~3-4MB (too large)
• After convert -resize 1280x720 -quality 85: ~200-250KB (well under 2MB limit)
• YouTube max thumbnail size: 2MB
• YouTube thumbnail dimensions: 1280x720 (16:9)
• Accepted formats: JPG, PNG, GIF

Example Prompts

Tech Demo Thumbnail

Create a YouTube thumbnail (1280x720) for a video titled "SpaceMolt - AI Agents in Multiplayer Space Games".
This is about a demo of SpaceMolt, a multiplayer space trading and mining game where AI agents autonomously play alongside human players.
The visual should be exciting and space-themed: spaceships, asteroids, neon glow, a dark cosmic background.
Bold text overlay: "SPACEMOLT" prominently, with smaller text "AI AGENTS IN SPACE GAMES" below it.
Include a bottom bar with "AI IN ACTION 7 FEB 2026" in bold.
Please include the Latent Space podcast logo in a corner — search the web for "Latent Space podcast logo".
Use vibrant sci-fi colors — electric blue, green, purple neon tones.

Academic Paper Thumbnail

Create a YouTube thumbnail (1280x720) for a video titled "RL via Self-Distillation (SDPO) Paper Reading".
This is an academic paper reading session about SDPO — Self-Distillation Preference Optimization.
The visual should be academic but engaging: neural network or brain visualization with mathematical formulas.
Bold text overlay: "SDPO" prominently, with smaller text "SELF-DISTILLATION PREFERENCE OPTIMIZATION" below it.
Include a bottom bar with "PAPER CLUB 12 FEB 2026" in bold.
Please include the Latent Space podcast logo in a corner — search the web for "Latent Space podcast logo".
Use deep blue, orange, and white color palette with a dark academic-themed background.

Troubleshooting

• "File is bigger than 2MB": Compress with ImageMagick convert -resize 1280x720 -quality 85
• Gemini generation takes long: Pro mode takes 30-45 seconds. Wait and check with a screenshot.
• Upload button not visible: Use the find tool to locate the hidden "Upload file" button by ref.
• File picker automation fails: Instruct user to manually select the file.