WebP is an image format developed by Google. It supports both lossless and lossy compression and, at comparable quality, is roughly 26% smaller than PNG and 25–34% smaller than JPEG. Its MIME type is image/webp, and every current mainstream browser supports it.

Sizes from 10 KB to 100 MB are available, for confirming browser support, testing WebP conversion pipelines, and verifying image-optimisation components.

Characteristics of WebP

Both lossless and lossy modes, chosen per use case
Supports both transparency and animation, covering what PNG and GIF each do separately
It uses a RIFF container, so identifying it from only the first four bytes risks confusing it with other RIFF formats
Older server-side builds of GD or ImageMagick may not support it

For a detailed comparison of PNG, WebP and AVIF, see PNG vs WebP vs AVIF — a thorough comparison.

📖 Where people get stuck

PNG, JPEG, GIF and WebP at sizes from 1 KB to 100 MB, for upload limits, thumbnail pipelines and exercising image libraries. What separates the formats is described above; what trips up an implementation is usually common to all of them.

Case	What happens	What to do
A small image exhausts memory	Memory follows decoded pixel count, not file size. A 20 KB PNG at 10,000 by 10,000 pixels asks for roughly 400 MB in RGBA.	Cap dimensions separately from bytes. You can read width and height from the header before decoding — `getimagesize()` in PHP, or in Pillow right after `Image.open()` and before `load()`.
Portrait photos display sideways	A camera does not rotate the pixels; it records which way up it was in the EXIF orientation tag. Anything that ignores the tag shows the sensor orientation.	Read the orientation before generating a thumbnail, apply the rotation for real, then clear the tag. Rotating while leaving the tag makes compliant browsers rotate a second time. Inspect a file with the EXIF viewer.
A conversion drops the animation and the transparency	A conversion routed through a browser canvas only ever holds one frame, so an animated GIF becomes a still of the first. Convert to JPEG and transparency flattens to white or black.	To keep the animation you need something that understands multiple frames — ImageMagick or libvips rather than a canvas. To keep transparency, target PNG or WebP.
A file that looks like an image is not one	Extension and `Content-Type` are both claims from the sender. An image with other data appended still opens normally in a viewer.	Check the leading bytes, then re-encode before storing. Decoding and writing back out discards both appended data and embedded metadata. The byte sequences are in the magic bytes reference.

One exception matters when serving user-submitted images as they arrive: SVG is not an image in the relevant sense. It is a document that can execute script, so serving it from your own origin opens a cross-site scripting path. Serve it from a separate domain, or contain it with Content-Security-Policy and Content-Disposition: attachment.

🖼️ WebP images

About WebP images

Characteristics of WebP

Related reference and articles

📖 Where people get stuck