Reduce image file size (disk space, not display dimensions)

Sometimes a clipped page or a pasted image is ~ 3000x3000px and 10MB, when all I really need is a small 500x500 .png or something (recipe images for example). I could go into ~/Dropbox/Apps/Joplin/.resources/ and mogrify a specific image id with imagemagick, but I don’t think that would reduce the file size on my already synced devices.

In any case, is there a way to reduce the disk space used by an imported & sync’ed image?

At the moment there’s currently no solution for this unfortunately.