Image optimization resize for uploads

I am running the GD bbPress Attachments 4.3 and am pleased with the plugin. Our members are uploading images that they take from their phones and may not be savvy tech users, so asking them to resize their images may not be productive. Is there an image optimization tool that you recommend with this plugin to downsize and optimize these attachments? Attachments may be regular jpg photos or photos of drawings.
Thank you.