Most email providers cap attachments at 20–25 MB (Gmail and Yahoo at 25 MB, Outlook at 20 MB). Modern iPhone photos typically range from 3 MB to 12 MB depending on mode, so a handful of attachments will hit the limit. The same problem appears everywhere: website uploads that reject large files, social media platforms that take forever to load your photos, cloud storage filling up faster than expected.

The solution is image compression — making files smaller without making them look worse. Here's what you actually need to know, explained without jargon.

Why Are My Photos So Large?
A digital photo is a grid of pixels, and each pixel stores color information. A single photo from a modern smartphone might be 4032 × 3024 pixels — that's over 12 million pixels. Each pixel needs at least 3 bytes (one for red, green, and blue), so the raw data is around 36 MB before any compression.

JPEG compression reduces this dramatically by discarding details that the human eye can't easily see. That 36 MB of raw data becomes a 3–6 MB JPEG. But even at 3 MB, a dozen photos will blow past most email limits.

What Compression Actually Does
Think of compression like summarizing a long document. A good summary preserves the key points while cutting the word count. Image compression does the same thing with visual information — it keeps the details that matter and simplifies or discards the ones that don't.

When you set a JPEG to "quality 80" (the default in CompactJPG), you're telling the compressor: "keep 80% of the visual information that matters most." The result is a file that looks almost identical to the original but is 40–70% smaller.

The Quality Sweet Spot
There's a quality sweet spot for most photos: somewhere between 70 and 85. Below 70, you start to notice artifacts — blocky patches, color banding, and blurry edges. Above 85, you're paying a steep file-size penalty for improvements that are nearly invisible.

Here's a rough guide:

Quality 85–95: For photos you plan to print or edit further. Minimal quality loss, but files are still relatively large.
Quality 70–85: The sweet spot for web, email, and social media. Files are 40–70% smaller than the original, and quality is excellent.
Quality 50–70: For thumbnails or where file size is the top priority. Noticeable quality loss on close inspection, but fine for small images.
Below 50: Only for extreme compression needs. Expect visible artifacts.
PNG vs JPEG: Which Should You Use?
The short answer: use JPEG for photos, PNG for graphics with text, logos, or screenshots.

JPEG was designed for photographs — images with smooth color gradients and lots of detail. It's excellent at compressing these while keeping quality high.

PNG was designed for images that need pixel-perfect clarity: logos with sharp edges, screenshots with text, or any image that needs transparency. PNG compression is lossless, meaning it never degrades quality, but it can't compress photos as efficiently as JPEG.

For web images, this matters a lot. A photo saved as PNG might be 5× larger than the same photo saved as a quality-80 JPEG, with no visible quality difference.

What About WebP?
WebP is a newer format developed by Google that aims to be better than both JPEG and PNG. At the same quality level, WebP files are typically 25–35% smaller than JPEG. It also supports transparency like PNG.

Today, all modern browsers support WebP, so it's a great choice for the web. CompactJPG can compress WebP images just like JPEG, using the same quality slider.

The Easiest Way to Compress Images
CompactJPG was built for exactly this use case. Here's how simple it is:

Drop your images on the page — or click to browse, or paste from clipboard.
Click Compress. That's it. The default quality (80) works for most images.
Compare the result using the side-by-side view if you want to check quality.
Download individual files or all at once as a ZIP.
And here's the important part: your images never leave your device. Everything happens in your browser using WebAssembly technology. No uploads, no servers, no privacy concerns. Just smaller images.

You can try the tool at https://compactjpg.com