A 100 KB PNG test file

About this file

A 100 KB test file in PNG format, sized to exactly 102,400 bytes. Free to download with no signup, for verifying upload limits and file-handling behaviour.

The MD5, SHA-1 and SHA-256 values listed above are the real digests of this file. Recomputing them after download confirms the transfer was not corrupted, and they double as known-good expected values when testing a hashing library.

What this size means in practice

100 KB sits at the boundary between "trivially small" and "realistic payload". It is close to the total transfer weight of a single lean web page and is a common target size for performance-conscious images.

It clears the sub-1 MB caps many applications impose, but it is still small enough that a naive load-everything-into-memory implementation works fine — so it is not the right size for proving that streaming is necessary. Pair it with 10 MB or larger to see the difference.

Getting a feel for this size

On a 10 Mbps link the transfer takes roughly 82 ms, and about 8 ms at 100 Mbps. Base64-encoded it grows to roughly 133 KB.

Estimating a photographic PNG at roughly 2 bytes per pixel, this size works out to around 51,200 pixels — about 261 × 196 px at a 4:3 aspect ratio. Compression varies enormously with image content, so treat this purely as an order-of-magnitude figure.

What to check for this format

PNG is lossless and carries an alpha channel. Every file starts with the fixed 8-byte signature 89 50 4E 47 0D 0A 1A 0A, followed by IHDR / IDAT / IEND chunks. The key question for upload validation is whether your code identifies the file by those leading bytes rather than by its extension.

• Whether the alpha channel survives resize and conversion — converting to JPEG destroys it
• Whether image libraries such as GD, ImageMagick, or sharp hit their memory ceiling — PNG memory use scales with decoded pixel count, not file size
• Whether metadata such as tEXt chunks is stripped — PNG has no EXIF, but text chunks can retain information