WhatsApp has updated policies which doesn't allow simple text to be shared along with Image or URL or Document.
You can send the image this way:
NSMutableArray *activityItems= [NSMutableArray arrayWithObjects:img, nil];
UIActivityViewController *activityViewController = [[UIActivityViewController alloc] initWithActivityItems:activityItems applicationActivities:nil];
activityViewController.excludedActivityTypes = @[UIActivityTypePostToWeibo,UIActivityTypePrint, UIActivityTypeCopyToPasteboard,UIActivityTypeAssignToContact, UIActivityTypeSaveToCameraRoll,UIActivityTypeAddToReadingList, UIActivityTypePostToFlickr,UIActivityTypePostToVimeo, UIActivityTypePostToTencentWeibo,UIActivityTypeAirDrop];
[self presentViewController:activityViewController animated:YES completion:nil];
Also you would need to set permission in Plist file for iOS9
<key>LSApplicationQueriesSchemes</key>
<array>
<string>whatsapp</string>
</array>