4:3 is not a mistake — it is a legacy spec
Where 800×600 still shows up
Some LMS uploaders, government forms, and email builders cap images at 800×600 or 4:3. Old PowerPoint themes are 4:3. If you submit a 16:9 photo, the form letterboxes or rejects the file. This page locks 800×600 so you stop guessing.
Not Instagram, not YouTube
Instagram will crop 4:3 oddly. YouTube thumbs want 16:9. Use 1080×1080 or 1280×720 for those. Keep 800×600 for the boring portals that never updated their HTML file inputs.
Email width
Many email clients display ~600–800px content columns. An 800×600 photo fills that column without forcing horizontal scroll. Compress after resize if the ESP has a 200KB image cap.
Print is a different job
800×600 is ~1 megapixel. It is weak for a poster. For print, keep a larger master and use a print-oriented resize guide. This preset is for screens with a 4:3 hole to fill.