Test images that behave like real ones
Solid-colour test files compress to almost nothing and never exercise your pipeline. These are real generated pictures: abstract art, gradients, textures, avatars, placeholders and more, so file sizes, colour content and aspect ratios vary the way user uploads do. Mixed sizes come from a range or from social and wallpaper presets, and mixed formats are drawn per file.
Reproducible batches
A batch is defined by its seed and settings. Item n always uses seed batchSeed-n, and its generator, size and format come from a stream seeded by the batch. Run the same configuration next week and you get the same pictures. The encoded bytes can differ slightly between browsers, because each browser ships its own PNG, JPEG and WebP encoders.
Upload-limit testing
Many application forms state a pixel size and a file-size window for photos and signatures, often a few tens of kilobytes. Set Fixed size, a target in KB and Pad to exact bytes to produce files that sit exactly on, just under or just over a limit. Always confirm the current limits on the official portal; they change.