Adding text is easy. Making it readable is the hard part
Every photo editor can put words on a picture. What none of them tells you is whether anyone can read those words once the picture is a thumbnail in a feed, a slide at the back of a room, or a phone screen in the sun. White text looks fine on the part of the photo you happened to place it on and disappears where a cloud or a bright wall runs behind it.
This page checks that for you while you edit. Around every letter it looks at the two pixels just outside the stroke, the part your eye uses to tell the letter from the background, and measures the contrast between the text colour and what is actually there, using the same formula as the WCAG accessibility guidelines. If more than 15% of that edge falls below 3:1, the minimum WCAG sets for large text, you get a warning and a suggestion.
How much a shadow, outline or box helps, measured
We put the same white bold caption on four parts of one landscape photo (a cloud, blue sky, a sandy path and dark heather) and measured the share of letter edges below 3:1 with each style. Lower is better:
| White text on… | Plain | Soft shadow | Outline | Box |
|---|---|---|---|---|
| Cloud | 97% | 10.5% | 0% | 1.4% |
| Blue sky | 79% | 28% | 0% | 1.5% |
| Sandy path | 48% | 10% | 0% | 0.6% |
| Dark heather | 30% | 6% | 0% | 0.6% |
Two things stand out. Plain white text failed even on the darkest part of the photo: the heather has light tips, and almost one letter edge in three landed on them. And the soft shadow, the default in most editors, was not enough on blue sky, where more than a quarter of the edge stayed weak. An outline or a box fixed every position. The outline is the stronger effect; the box is the calmer one and suits longer captions, quotes and slides.
These numbers come from one photo, so treat them as a guide rather than a rule. That is why the check runs live on your own picture: move the text and the verdict updates.
Placing text so it works
- Look for an even area. Sky, water, a wall or an out-of-focus background. Busy texture such as leaves, gravel or crowds breaks letters up even when the average colour contrasts well.
- Keep it short and big. Text that is 6 to 10% of the image width is still legible when the picture is shown small. Long sentences belong in the post, not on the image.
- Leave a margin. Social apps crop and round corners and lay buttons over the bottom of pictures. Keep text away from the outer 5% of the frame.
- Match the weight to the job. Bold sans for headlines and thumbnails; serif or regular weight for quotes and invitations, ideally with the box.
Your original, kept intact
The preview is scaled down so it stays fast, but the download is drawn on the original pixels: a 4000-pixel photo comes back as a 4000-pixel photo, with the text in the same place it had in the preview. A JPEG is saved as a JPEG at high quality, a PNG stays a PNG (transparent areas stay transparent, so you can caption a logo or sticker), and a WebP stays WebP. Phone photos are turned upright from their orientation tag first, so the text is not drawn sideways. As with every tool on this site, the photo never leaves your device.
For a classic top-and-bottom caption, the meme maker is quicker. To mark ownership on many photos at once, use add watermark to image. If the picture is going to a specific platform, size it first with the social media image resizer.