I've not been able to pin down whether the photos uploaded from an iPhone to photo stream are full resolution. I saw mention that they are downloaded in full resolution to OSX machines and not iOS. But not how they have been uploaded.
Resolution of iPhone photo stream upload!
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Related Solutions
A photo stored in the Camera Roll is permanently stored on your device (until you delete it). Only 1,000 photos are saved in the Photo Stream on an iOS device, so if enough photos are uploaded to your Photo Stream the old ones will be purged. (But a Mac or PC will save all of the photos in your Photo Stream by default.)
According to Apple, the downscaling does only apply on iOS devices — if you have Photo Stream set up on your computer, those photos will be full-resolution.
On your Mac or PC, your photos are downloaded and stored in full resolution. On your iPhone, iPad, iPod touch, and Apple TV, your Photo Stream photos are delivered in a device-optimized resolution that speeds downloads and saves storage space.
Yes — to delete multiple photos, just tap the action button in the upper right corner, select some photos, and tap the Delete button.
How Photo Stream Works
If you have Photo Stream enabled on both iPhone and iPhoto, any picture you take on iPhone is automatically uploaded to Photo Stream, and the automatically downloaded to iPhoto. iPhoto must be open for this to occur (but don't worry, the photos stay in Photo Stream for 30 days or until 1000 more pictures are taken, whichever comes first, so you don't have to have iPhoto running constantly).
Uploading Photos to Photo Stream
Photo Stream only uploads from iPhone while connected to WiFi. Occasionally a picture is missed, and as of now (August 2013) videos are never uploaded. There is no way to trigger an upload later if a photo fails to upload to Photo Stream. You can, however manually sync iPhone with iPhoto to sync videos as well as any missed photos.
Syncing iPhone with iPhoto Manually
Plug iPhone into your Mac then in iPhoto, click on your device in the left sidebar. There will be an Import button. It will automatically skip any photos previously imported from Photo Stream. Once imported you can choose whether to remove them from Camera Roll on the phone. If you do this, make sure you are syncing them back to iPhone in iTunes if you want them on the phone in albums.
Deleting Photos
Deleting from Photo Stream
When you delete a photo from Photo Stream, it removes it from Photo Stream entirely. If it was already downloaded into iPhoto it will remain there under the (MonthName Year) Photo Stream album, but not in Photo Stream itself.
Deleting from Camera Roll
When you delete a photo from Camera Roll it removes it from that area but does not delete it from Photo Stream.
Best Answer
Yes, I can confirm to you they are exact the same. Photo's are exact the same format and file-size.
You can also verify this yourself by connecting your iPhone to your PC using the USB cable and get one picture from it. Check the size, resolution and format. Now open your Photostream and do exact the same.