PhotoPenguin App - PhotoPenguin is a completely free batch photo editor with support for cropping, resizing, adding watermarks, and converting photos to other formats. It works on the user's device, using the capabilities of modern browsers.
TinyJPG - Compress JPEG images with perfect quality and file size
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
Promo Instant Image Resizer - Automatically optimize images for web & social media (free!)
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats
Compressor - Compressor adds power and flexibility to Final Cut Pro X export.