Resize Images on Server

We require a coder to run a script to resize all jpeg thumbnail images in several folders on a Linux server. The current thumbnails of approximately 150 x 200 need to be increased in height to 502 pixels with the corresponding side adjusted automatically to preserve the aspect ratio of the the original thumbnail image. The increase in size needs to also include a sharpening process to reduce the loss in quality. The existing file needs to remain unchanged and the new jpg file created with the same file name with an underscore appended to the name. There are approximately 15 subfolders with 20,000 jpeg files in each that require conversion.