Handle image optimization during a CMS migration by auditing your current image library, cleaning up files and alt text, then compressing and serving responsive sizes in the new system. A CMS migration, the move of content from one content management system to another, is the right time to fix heavy images rather than copy them as-is.
Start with an inventory of what you have. Many sites carry duplicate logos, unused banners, and oversized photos. Removing that weight before the move makes every later step faster and simpler.
Official resources:
- Verify image filenames, alt text, and structured data requirements — Check Google's official requirements for making migrated images crawlable and eligible for image search.
- Follow the site move procedure for changed URLs and redirects — Use Google's migration checklist to map redirects and monitor indexing when CMS URLs change.
Table of Contents
- What to Audit Before You Move?
- How Should You Prepare Image Files?
- How Do You Keep Image Traffic and Links Working?
- What to Check After Launch?
What to Audit Before You Move?
List every image folder, upload directory, and hotlinked file used by the old site. Note file size, dimensions, format, page location, and whether the image still serves a purpose. Large hero images, slideshows, and blog uploads often hold the most waste. Check filenames, titles, captions, and alt text.
Alt text is the short written description that screen readers and image search use to understand a picture. Clear names like oak-dining-table.jpg help more than IMG_4821.jpg. Decide what to keep, replace, or delete. Delete unused files, duplicates, and tiny thumbnails that the new theme will rebuild. Keep original high-quality versions in a separate archive so you can create new sizes without quality loss.
How Should You Prepare Image Files?
Resize images to the largest size the new design actually displays. A 5,000-pixel-wide photo used in a 1,920-pixel-wide banner adds load time with no visible benefit. Export at that display size and compress to reduce bytes while keeping edges and text sharp.
Use a consistent workflow for each keeper image: Test a sample batch before processing thousands of files. Compare sharpness on a laptop and a phone, then adjust compression once and apply the same settings to similar images. This prevents blurry logos and over-compressed product details.
- Rename the file with short, plain words separated by hyphens.
- Compress the image and save a modern format when your new system supports it.
- Create smaller versions for phones and tablets if your theme does not create them automatically.
- Write specific alt text that describes what the image shows and why it matters on the page.
How Do You Keep Image Traffic and Links Working?
Keep image URLs stable when you can. If paths must change, map each old image address to its new address and redirect the old address to the new one. A redirect is an automatic forward that sends visitors and search engines from one URL to another. Carry over alt text, captions, and titles during import.
Migration tools sometimes drop these fields or place them in the wrong database field. Spot-check galleries, featured images, and product photos, where missing descriptions hurt access and discovery most. Update sitemaps, feeds, and structured data after the move. Image sitemap entries, Open Graph tags, and product markup should point to live files on the new domain. Broken image links in these places can reduce clicks from image results and social previews.
What to Check After Launch?
Crawl the new site for missing images, wrong sizes, and slow pages. Look at templates separately: home, article, product, category, and search pages often load different image sizes. Fix template-level problems first because one fix can improve hundreds of pages.
Measure load behavior on real phones and slower connections. Pay attention to large images below the fold, autoplay sliders, and background videos with poster images. Delay loading for offscreen images so the top of the page appears sooner. Re-run your image crawl two weeks after launch and fix any new 404s the same day.
