Find the actual limit first
Email providers and upload forms impose different maximum sizes, and the limit may apply to one file or an entire message. Read the error or form instructions before choosing an arbitrary compression setting. Keep space for other attachments and any encoding overhead.
If the limit applies to an entire set of files, compressing each image separately is not always enough. Add up the outputs and leave a sensible buffer.
Reduce dimensions before extreme quality cuts
A camera image might be thousands of pixels wide even when its recipient will only view it on a phone. Exporting at a width appropriate to the destination often removes more unnecessary data than pushing JPG quality to its minimum. Preserve aspect ratio and inspect important details.
For receipts or scans with small print, readability matters more than minimizing bytes. Check the smallest characters after exporting.
Understand the quality slider
Lower JPG or WebP quality typically reduces file size at the cost of more artifacts. The same setting can produce different sizes for a simple picture and a highly textured one. Start in a moderate-to-high range, compare the result, and reduce gradually if the size still exceeds the limit.
Some files may become larger after conversion or recompression, especially when the source was already well optimized. Do not assume every re-save is an improvement.
Choose outputs that the form accepts
Many forms explicitly accept JPG and PNG, while others accept WebP as well. Do not upload a renamed extension; use a real converter when a different codec is needed. For transparent graphics, JPG will replace transparency with a solid background.
For a multi-image upload, keep consistent dimensions and naming so you can match every result back to its source.
Test before sending
Open one compressed image at normal viewing size and zoom into high-detail areas. Check that embedded text remains legible, the subject has not been cropped, and orientation is correct. When submitting formal documents, retain the original scan separately.
If the upload still fails, confirm its pixel-dimension restriction too. Some services enforce both bytes and resolution.
Privacy note
Browser-side image tools can process standard image data locally, but third-party assets or services can have different practices. Read a tool’s own privacy explanation, and avoid uploading sensitive records into unknown online converters. Download and verify your export before deleting anything.
Work through a real limit scenario
Suppose a submission accepts files up to 5 MB each. You have a 9 MB JPEG photo and a 600 KB PNG screenshot. The photo alone needs optimization; converting the screenshot just because it is PNG may be unnecessary. Export a smaller-width copy first, then compare one or two JPEG quality levels. The output must remain below the cap and remain legible.
If you do not know whether the image is oversized in pixels or simply inefficiently encoded, consult the resizing guide. The format comparison explains why PNG is often appropriate for screenshot text even when it produces a larger file.
Verification checklist for forms
Check the number of selected files, each exported name, exact bytes and supported extensions before submitting. Some forms also reject unusual pixel dimensions or do not accept transparent WebP. Avoid overwriting the camera original, because later compression passes starting from a degraded JPEG compound artifacts.
When the submission asks for PDF instead of images, converting each photo independently may not fix a large PDF. Start with the PDF email attachment guide to understand embedded pages and document preservation.