Compression is a balance between file size and the detail the image needs to communicate. The best setting depends on the subject and destination.
Choose a suitable format
JPEG and WebP work well for many photographs. PNG is useful for sharp graphics and transparency but can be larger for photos. Converting an already compressed image to PNG does not recover detail that was previously lost.
Reduce unnecessary dimensions
If a website displays a photograph at a modest size, an extremely large source may be unnecessary. Resize first while preserving aspect ratio. Keep enough pixels for the actual use, especially if the image will be printed or cropped later.
Adjust quality gradually
Use Compress Image with a target size or quality control. Target size is a goal, not a guarantee for every image and format. Compare text, hair, edges and gradients in the exported file. Strong compression can introduce blocks or ringing.
Save a separate output
Keep an original and avoid repeatedly editing the compressed copy. Confirm the actual file type and byte size after downloading. Some portals accept only specific formats even when other formats are smaller.