Although WPtouch defines appropriate thumbnail and featured image sizes, WordPress only applies these to media added after WPtouch is activated. Old images must be re-processed to produce appropriately sized content using a tool such as the Regenerate Thumbnails plugin. We recommend making a backup of your site before regenerating your thumbnails.
Today's high-DPI smartphone displays require higher resolution images to produce a crisp appearance. To provide this, WPtouch registers a larger thumbnail size with your WordPress installation. When an image with WPtouch thumbnail size is unavailable, the next smaller size is used. Reprocessing your media will ensure correctly-sized images are available.
Excessively large images
Similarly, images added to your site before installing and activating WPtouch may not have the appropriate image size available. WordPress returns the next-closest image, which may be a high-resolution version. Regenerating your post-thumbnails will ensure correctly-sized images are available for use in WPtouch.