The three formats worth knowing
Image formats are not interchangeable, and picking the wrong one is a common cause of both bloated files and rejected uploads.
JPEG, for photographs
Lossy, which means it permanently discards detail in exchange for a much smaller file. That trade-off suits photographs, where the discarded detail is subtle gradation your eye barely registers. It has a quality dial, so it can be tuned to hit a size target, the reason essentially every official portal asks for it.
Its weakness is sharp edges. Text and line art in a JPEG develop visible fringing, which gets worse each time the file is re-saved.
PNG, for graphics and transparency
Lossless: every pixel is preserved exactly. Excellent for screenshots, logos and diagrams, where large areas of flat colour compress extremely well. It is the only one of the three in common use that supports transparency.
Its weakness is photographs. With no two adjacent pixels alike, there is nothing to compress, and a photo saved as PNG is often ten times larger than the same photo as JPEG.
WebP, for the web
Roughly 25–35% smaller than JPEG at the same visual quality, with support for transparency, and supported by every current browser. Ideal for a website. Poor for an official upload, because portal validators lag years behind browsers.
The HEIC problem
This deserves its own section, because it accounts for a large share of "my photo will not upload" frustration.
iPhones have saved photos as HEIC by default for years. It is an excellent format, better compression than JPEG at the same quality, and almost nothing outside Apple accepts it. Worse, it looks like a normal photo everywhere on the phone, so there is no clue anything is different until a form silently refuses it.
Two fixes:
- Change the setting. Settings → Camera → Formats → Most Compatible. New photos will be JPEG. This is the permanent fix.
- Convert an existing photo. Emailing it to yourself, or sharing it through most apps, converts it to JPEG on the way out.
Safari opens HEIC by itself; in other browsers The Daily Toolbox reads it with a small HEIC decoder that runs in the page, so the photo still never leaves your device (a full-size photo takes a few seconds). Many other sites convert HEIC by uploading your photo to their server; for an identity document, that is worth knowing before you click. For several photos at once, use HEIC to JPG.
Quick reference
| You have | You need | Use |
|---|---|---|
| A photo for an official form | Acceptance | JPEG, always |
| A screenshot with text | Readable text | PNG |
| A logo with a transparent background | Transparency kept | PNG |
| Photos for your own website | Fast pages | WebP |
| A HEIC from an iPhone | Anything to accept it | JPEG |
Converting and resizing together
Set a size limit in the options above and the conversion and compression happen in one pass, so the file comes out upload-ready. If you also need specific dimensions, use the resize tool, it can change format at the same time.