Poll deleted since this is a technical question rather than an opinion and it can be answered without votes.
If you email the pictures, you can send them at the full resolution. Just select the largest size on the pop up. The messaging app will compress them so use email or DropBox instead if you don't want to lose any quality.
If you want to actually increase the photo size and zoom in, you'll have to zoom and take a screenshot or use an app. The image quality will be decreased if you do this.