← Image resizer

Resize an image with curl

Resize an image to fit inside a box, fill it and crop, fit and pad, or stretch to exact dimensions. Here is the whole call with curl, with the output it produced when we ran it.

Before you start

An API key. Create a free account; it comes with free tokens every month. Put the key in an environment variable so it stays out of your code: export BLOODWEB_KEY=your_key
curl 7.76 or later (for --fail-with-body, which makes curl stop on an error and still show the reason).
The input file in the same folder: photo.jpg. Use your own; that is the name the code expects.

The code

Save it as image-resize.sh and run bash image-resize.sh.

curl -sS --fail-with-body \
  -H "Authorization: Bearer $BLOODWEB_KEY" \
  -F file=@photo.jpg \
  -F width=800 \
  -F height=800 \
  -F fit=cover \
  https://bloodweb.net/api/v1/image-resize \
  -o thumb.jpg

What you get

Tested 19 October 2026: this exact code ran against our test copy of the API, which runs the same service code as bloodweb.net, and produced this.

It writes thumb.jpg: a JPEG image, 800 × 800 pixels, 15 KB.

Change the call

Every option the Image resizer takes. Add or change them the same way as the ones in the code.

width: Target width in pixels. Give width, height or both.
height: Target height in pixels.
fit: inside: fit within the box, keeping proportions. cover: fill the box and crop the overflow from the centre. pad: fit within the box and fill the rest with the background. exact: stretch to the box. cover, pad and exact need both width and height. One of: inside, cover, pad, exact.
gravity: Which part of the image to keep when fit=cover crops it. One of: center, top, bottom, left, right, top-left, top-right, bottom-left, bottom-right.
upscale: Allow enlarging an image smaller than the box (inside and pad).
to: Output format. Defaults to the input format (HEIC becomes JPG, ICO becomes PNG). One of: jpg, png, webp, avif, gif, tiff, bmp.
quality: For JPG, WebP and AVIF.
background: Padding colour for fit=pad, or "transparent" where the format allows it.
strip: Remove metadata.

If it fails

A failed call is not charged. The answer is JSON with an error object; curl stops with an error, and that JSON lands in thumb.jpg instead of the result, so open it as text to read the reason. The usual ones:

401 missing_key or invalid_key: BLOODWEB_KEY is not set in the shell that runs the code, or the key was revoked.
415 unsupported_type: the file is not a type this service reads. The type is read from the file itself, so renaming a file does not change it.
413 file_too_large: the file is over the limit on the service page.
402 insufficient_tokens: the balance does not cover the call. Top up in the dashboard.
429 rate_limited: too many calls at once. Wait the seconds in the Retry-After header and send it again.

Every code and its fix is in the docs.

The Image resizer page: every option, the limits, and Try it now in your browser.
Getting started: keys, errors and rate limits for all the services.