Short answer
Browser-based image compression is practical for ordinary publishing assets, but very large decoded images can consume substantial device memory before an output file is created.
When this applies
Use a smaller source or resize first for very high-resolution photos, scans, and images with many megapixels, especially on mobile devices.
Practical review steps
- Check pixel dimensions as well as file size.
- Process one large image at a time on lower-memory devices.
- Keep a smaller working copy for web publication rather than repeatedly editing the camera original.
Check the actual color pair
Use the free Image Squeeze with the foreground and background colors from the real component. It provides an immediate AA and AAA ratio check in the current browser tab.
Source and limit
For the formal requirement, review W3C's WCAG contrast minimum guidance. A ratio result checks a color pair; it is not a complete accessibility audit.