For over a week there has been an issue where uploading images to Google plus has been reducing the size of the image to a thumbnail size of 200 x 320. It seems to be only happening on my Nexus 7, and seems to have started randomly around the 15th of September as far as I can tell. The only thing I can recall related to image size was changing a setting recently to upload images at full resolution instead of 2048 max. Hopefully this will be fixed soon, but it doesn't seem to be an issue that others are seeing so who knows.