Compression is not a format change
You already have a JPEG. Compressing it means decoding and encoding again at a lower quality (or with a smarter encoder at similar quality). The output is still .jpg. That is what you want when a website’s file picker says “JPG/PNG only” and your 8 MB phone photo is rejected. Converting to WebP might be smaller, but the picker will bounce it. Compress JPG is the compliant path.
The cost is generation loss. Each full recompress can add blockiness, especially around text and sharp edges. If you still have a high-quality original or a RAW, compress from that once. Do not download, compress, upload, download, compress again. WhatsApp is infamous for this spiral; do not imitate it.
Quality, chroma, and when to resize first
Quality numbers are not comparable across tools, but the idea is stable: high 80s look close to the original for most photos; 70s are a common web default; below 60 you are in “it will do for a thumbnail” territory. Skies, gradients, and skin show banding first. Screenshots of text should rarely be compressed as JPEG at all—use PNG.
Resolution is the other lever, and it is often the bigger one. A 4000-pixel JPEG displayed at 800 CSS pixels is wasting 25× the pixels. Resize to 2× the display size (for retina), then compress. Compressing a 12-megapixel file to quality 40 still leaves a lot of pixels to encode. For ID photos, the form usually wants something like 200–600 pixels on a side—resize first or you will fight the quality dial forever.
Progressive JPEG (loads blurry then sharp) is a nice extra on the web; not every encoder emits it. Do not worry if the output is baseline sequential—portals do not care.
What ToolPin does with the file
Recompression runs in the tab. Passport photos, medical images, and unpublished shoots are not uploaded. 250 MB limit. No account, no watermark. Canvas encode typically strips or reduces EXIF. That can be a privacy win (GPS gone) and a surprise if a lab used EXIF DPI. Orientation is usually baked in, which prevents sideways uploads.
If the file barely shrinks, it was already crushed, or it is mostly incompressible noise. Try resize. If it shrinks to a blotchy mess, you aimed too low—raise quality or start from a better original.
A practical target list
Email: under 1–2 MB per image is polite. Many portals: 200–500 KB. Hero images on a site: as small as you can without visible damage at 2× device pixel ratio; consider WebP/AVIF if you control the HTML. Print: do not compress for a 300 DPI poster; you need pixels more than a small file. And if the JPEG contains a document scan, consider whether PDF is the better share format than a crushed photo of text.