How to compress a photo for an online form

A phone photo is usually 2–6 MB and 3000–8000 pixels wide. Application portals often ask for a passport-style photo under 50, 100 or 200 KB, and a signature under 20 or 50 KB. They do it to keep their storage and review screens manageable, and because a face for an ID card does not need 12 megapixels.

A portal can reject a file for several reasons, and the error message does not always say which:

• File size over the limit (the most common).
• Wrong format: many accept only JPG/JPEG, some also PNG or PDF. HEIC from an iPhone is almost always refused.
• Pixel dimensions outside a required range, for example “between 200 × 230 and 300 × 350 pixels”.
• Too small: some portals also set a minimum, like “at least 10 KB”.

Read the instructions for all four before you start; it saves several rounds of trial and error.

Strictly, a kilobyte (KB) is 1000 bytes and a kibibyte (KiB) is 1024 bytes. Many systems still use “KB” for 1024 bytes. So a “100 KB” limit means either 100,000 or 102,400 bytes depending on who wrote the portal, and a file of 101,000 bytes passes one and fails the other.

Windows Explorer, for example, shows sizes in 1024-byte units while labelling them KB, and rounds up; macOS Finder counts in 1000s. That is why a file can look like “98 KB” on one computer and be rejected anyway.

The safe approach is to aim under 1000 × N bytes. KiteConvert’s compress-to-size tools do exactly that: a “100 KB” result is at most 100,000 bytes, which passes both interpretations, and the exact byte count is shown so you can check.

There are two ways to make a JPG smaller, and the order matters.

1. Reduce the pixel dimensions. A form photo is shown in a box a few hundred pixels wide. A 4000-pixel photo spends almost all its bytes on detail nobody will see. Resizing to the size the portal asks for (or around 600–1000 px on the long side if it does not say) cuts the file by 90% or more with no visible change at that size.
2. Lower the JPEG quality. Once the dimensions are sensible, quality 70–85 usually fits under 100 KB. Going below about 50 brings visible blocks around faces and edges.

If you only lower quality on a full-size photo, you end up with a large picture full of artefacts. If you resize first, you get a small picture that looks clean. Our compress-to-size tools try quality first and then scale down in steps only when needed, and report what they did, for example “Quality 62, resized to 1600 × 1200”.

1. Crop the photo first so it shows what the form asks for, usually head and shoulders on a plain background. Cropping removes pixels the portal would waste bytes on.
2. Open the compress-to-size page for your limit (50 KB, 100 KB, 200 KB…), or enter any target in the tool.
3. Drop the photo. HEIC, PNG and WEBP are accepted and come out as JPG, the format portals expect.
4. Check the result: the size in bytes, the quality used and the final dimensions. Zoom in on the face.
5. If the portal also requires exact pixel dimensions, resize to those first with the resize tool, then compress.

The photo is processed on your device and never uploaded, which matters for ID photos and signatures. GPS location is removed by default.

Signatures often have the tightest limit (10–50 KB). They are easy to get small if you prepare them well:

• Sign with a dark pen on plain white paper, and photograph it in daylight without shadows.
• Crop tightly around the signature. Most of the bytes in a signature photo are in the empty paper around it.
• Resize to the dimensions the form gives, often around 140 × 60 pixels or similar; if none are given, 400–600 px wide is plenty.
• Save as JPG. A clean black-on-white signature fits into a few kilobytes.

For scanned certificates and ID cards that must be a PDF under a limit, use JPG to PDF under N KB. It compresses the images just enough for the whole PDF to fit, and tells you if the text would become unreadable at that size.

Every portal sets its own rules, so always follow the instructions on the form itself. Common patterns:

• Passport-style photo: JPG, 20–200 KB, a few hundred pixels wide, plain light background, face covering a set share of the height, taken recently.
• Signature: JPG, 10–50 KB, wide and short, black or blue ink on white.
• Document scans: PDF or JPG, 100–500 KB per file, readable at 100% zoom.
• Résumé photo or profile picture: JPG or PNG, often up to 1–2 MB, square crop.

Some portals ask for dimensions in centimetres together with a DPI value. Multiply: 3.5 cm at 300 DPI is about 413 pixels (3.5 ÷ 2.54 × 300).

• Renaming photo.heic to photo.jpg. The name changes, the contents do not, and the portal rejects it or shows a broken image. Convert it instead.
• Taking a screenshot of the photo. It adds the phone’s interface and produces a PNG, often larger than the original.
• Compressing a photo twice in different tools. Each lossy pass adds artefacts. Start from the original every time.
• Aiming exactly at the limit. A file of 100,300 bytes fails a 100,000-byte check. Leave a margin, or use a tool that targets 1000-byte kilobytes.
• Forgetting the minimum size. If the portal says “10–100 KB”, a 6 KB result also fails; choose a larger target.

On a Mac, Preview can do both steps: Tools › Adjust Size to change dimensions, then File › Export with the JPEG quality slider, watching the file size shown in the dialog. On Windows, Paint’s Resize button reduces dimensions and File › Save as › JPEG picture saves a JPG, though Paint gives no quality control. Both work for one photo at a time; neither aims at an exact byte limit, so check the size afterwards.