You can use mogrify to process all images in a directory. See http://www.imagemagick.org/Usage/basics/#mogrify
Example - say you have folder1 with all your images. Then create a new directory folder2 to hold all the processed image, if you do not have a backup of your folder1. Then use mogrify. I am assuming you are on IM 6.
Code: Select all
mogrify -path path2/folder2 -resize 800x800 *
It would help if you always provide your IM version and OS/platform. Also please explain what you mean by "800 wide and keep the aspect ratio tall size". If you have to test for portrait vs landscape and need the width to always be 800 in either case, then you will need to have a script loop over all the images in the directory and a conditional test, since the resize arguments may need ^ added for one and not the other depending upon your meaning.
Also you have not said what format images are being process and what format you want them saved. This is important if you are going from jpg to jpg, since it will lose quality and likely need for you to add -quality XX.
Are all the images sRGB or are some of them CMYK? If true, this will also require scripting to handle these two cases, since it is best to convert all images to sRGB and add an sRGB profile, so that all viewer will display the images the same.
So more information is needed to confirm my mogrify command.