Image compression is powerful but easy to misuse. Avoid these common mistakes for optimal results.
1. Using CSS to Resize Large Images
Don't upload 4000px images and resize with CSS. Users download the full file anyway. Always resize to display dimensions before uploading.
2. Over-Compressing Critical Images
Quality 50-60% introduces visible artifacts. Use quality 75-85% for the sweet spot—significant savings without quality loss.
3. Using PNG for Photographs
PNG produces huge files for photos. A 150KB JPEG can be 2MB as PNG. Use JPEG/WebP for photos, PNG only for graphics and transparency.
4. Forgetting Metadata
EXIF data, thumbnails, and GPS add 50-200KB per image with no benefit. Strip metadata before publishing. Most compression tools do this automatically.
5. Not Testing at Display Size
Images look fine at display size but show artifacts when pixel-peeping at 100%. Always evaluate at actual display dimensions.
6. Inconsistent Compression
Establish standards: hero images 85%, products 85%, thumbnails 80%, backgrounds 75%. Use batch processing for consistency.
7. Serving Desktop Images to Mobile
Implement responsive images with srcset. Mobile users shouldn't download desktop-sized files.
8. Lazy Loading Everything
Only lazy load below-the-fold images. Above-the-fold images must load immediately or you hurt LCP scores.
9. Omitting Image Dimensions
Always specify width and height to prevent layout shift: <img src="image.jpg" width="800" height="600">
10. Ignoring Modern Formats
WebP is 25-35% smaller than JPEG with broad support. Implement with picture element for fallback: <picture><source srcset="image.webp" type="image/webp"><img src="image.jpg"></picture>