Pixelwelt

Image Sizes on Demand generates sizes of an image at the moment they are requested. It tries to generate the new size 
from the original image, if it exists. This means you don’t need to regnerate all your images if you add new iamge 
sizes.
<h3>Arbitrary section</h3>

Image Sizes on Demand

Creates the new size of an image, if it is requested and does not already exist.

YoOhw Studio

Thumbnail Manager helps you take back disk space from oversized Media Libraries.
What it does 
– Prune Files: Select the image sizes you want to KEEP. The plugin scans your <code>/uploads/</code> folder and targets all non-selected registered sizes for removal. It shows a dry-run summary first, then lets you delete in batches with a live progress bar. 
– Orphan discovery: Finds on-disk files that match <code>-WxH</code> patterns (including <code>.jpg.webp</code>, <code>.bak.jpg</code>, retina <code>@2x</code>, and duplicate <code>-1</code> suffixes) even if those sizes are no longer registered. Aggressively deletes any <code>-WxH</code> files that don’t exactly match the sizes you chose to keep (use with care). 
– Subfolder scope: Limit scans to a specific year/month inside <code>uploads/</code> for faster, safer runs on large libraries. 
– Thumbnail Sizes: Choose which sizes should be generated for future uploads. Disabled sizes won’t be created at upload time (and are hidden from size pickers).
What it doesn’t do 
– It does not regenerate thumbnails. Use a regeneration plugin if you need to rebuild sizes after changing settings. 
– It never deletes original full-size images.
Who is it for? 
Site owners, editors, and developers who’ve accumulated many custom image sizes (themes, page builders, sliders) and want to reduce storage bloat safely.
<h3>Features</h3>
<ul>
<li>Two-tab UI: Prune Files & Thumbnail Sizes</li>
<li>Dry-run mode with sample matches before any deletion</li>
<li>AJAX progress bar and batch deletes to avoid timeouts</li>
<li>Orphan <code>-WxH</code> discovery report and delete found dimensions</li>
<li>Limit to subfolder (All, year, or year/month)</li>
<li>Disable sizes for future uploads (does not unregister core sizes; simply prevents generation)</li>
<li>Hides disabled sizes from Media size dropdowns (optional filter)</li>
<li>Works per-site on single and multisite (run on each site as needed)</li>
</ul>
<h3>Usage</h3>
<h3>Prune Files</h3>
<ol>
<li>In the table, check the sizes you want to KEEP (e.g., <code>thumbnail</code>, <code>medium</code>, <code>large</code>, and optionally <code>medium_large</code>).</li>
<li>(Optional) Choose a subfolder (e.g., <code>2024/11</code>) for a quicker, safer trial run.</li>
<li>Make Orphan discovery ON to see a report or do a deletion of found dimensions.</li>
<li>Click Run with Dry-run selected to preview matches.</li>
<li>Review results → switch to Delete when you’re confident.</li>
</ol>
Tip: Enable Orphan discovery only when you want to remove any extra <code>-WxH</code> sizes not exactly matching your KEEP list (great for cleaning legacy sizes like <code>-1200x860</code> or <code>.bak.jpg</code> files).
<h3>Thumbnail Sizes</h3>
<ol>
<li>Uncheck any sizes you no longer want generated for future uploads.</li>
<li>Click Save changes. 
(This prevents those sizes from being created going forward; existing files are unaffected until you prune them in Prune Files Tab.)</li>
</ol>
<h3>Technical Notes</h3>
<ul>
<li>Prevent generation via: <code>intermediate_image_sizes_advanced</code> (removes disabled sizes at upload time). </li>
<li>Optionally hide in UI via: <code>image_size_names_choose</code> and reduce the base list via <code>intermediate_image_sizes</code>. </li>
<li>Auto-scaled big image can be disabled with <code>big_image_size_threshold</code> if desired (not enabled by default). </li>
<li>Requires capability <code>manage_options</code>.</li>
</ul>
<h3>Privacy</h3>
This plugin does not collect personal data or send data to external services. It only reads and modifies files within your <code>/uploads/</code> directory based on your actions.

Thumbnail Manager

Clean up unused thumbnails with progress; find orphan -WxH files; disable sizes for future uploads.

Image Sizes on Demand vs Thumbnail Manager