Forms refuse the file, the print comes out blurry, the picture has a white box instead of a transparent background: most of these problems come from choosing the wrong format or size. Here is what each one is for.
JPEG, PNG and HEIC
JPEG is the universal format for photos: small files, accepted everywhere, but a little quality is lost every time it is re-saved. PNG keeps every pixel and supports transparency, at a larger size — use it for cut-outs and graphics. HEIC is what recent iPhones shoot; it is efficient but many forms and websites do not accept it, so convert to JPEG before uploading.
Pixels and dpi
The pixel dimensions are the real size of a picture. Dpi only matters for printing: at 300 dpi, a 10 × 15 cm print needs about 1200 × 1800 pixels, and a 35 × 45 mm ID photo needs 413 × 531. Changing the dpi value without changing the pixels changes nothing on screen.
Sizes forms and prints ask for
Online forms often specify a pixel size (600 × 600 px is common), a format (JPEG) and a maximum weight (for example 240 KB). Printers want enough pixels for the size at 300 dpi. The ID photo tool exports both; the editor lets you resize and re-export any picture.
Converting and compressing
Convert HEIC to JPEG once, from the original. When a form imposes a weight limit, reduce the pixel size before increasing the compression: a smaller, clean picture beats a large, blocky one. Keep the original untouched.
Checklist
- JPEG for photos, PNG for transparency, no HEIC in forms
- Think in pixels; dpi is for printing
- 300 dpi for prints: 1200 × 1800 px for 10 × 15 cm
- Reduce the size before compressing harder
- Always keep the original file
When in doubt: a JPEG at the pixel size the destination asks for, exported from the original file. That covers nearly every form, print and profile.
