A 4 MB phone photo becomes about 600 KB at 2048 px with no visible loss on a screen. That means 15 to 20 photos fit in a single Gmail message instead of 5. Drop them all, download the ZIP, and attach it.

If the receiver needs to print, keep the pixels: choose the Exact size mode on the homepage and set only a file cap of 2 MB instead.

Try it on your own photoDrop a photo at the top of the page. Ten seconds later it's sized, sharpened and ready to post.
Compress a photo