Welcome to Android Central! I assume you're talking about imo, correct? So you want to know how to save photos sent to you on your imo app? Try long-pressing the photo and see if any options appear. If you're still stuck, try emailing their support: android@imo.im
Send imo images to your gmail from your mobile.
Preview the images in your gmail inbox from PC and Right click on image and use "save image as...." option to save them on your PC.