Quality photos end up blurry

[raidesuu]

I've found a bunch of other threads with this similar issue but none that have been resolved.
I have had an S3, S4 (now I'm back to iPhone) but I currently have a Samsung Galaxy Note Tab.

When photos from any of my previous galaxy phones, and now my tab are uploaded to Instagram, Facebook or even Dropbox the image ends up being blurry/unclear. I understand that the images are being compressed but all the other forums are saying "it's an IG issue" or "it's a facebook issue" that needs to be fixed. Obviously it's an issue with the devices.
I took with my DSLR and saved on my tablet to use as my background. It looked great. I changed it a couple of times but recently tried save that exact same photo as a background again and guess what?! It looks terrible! The great quality just disappeared. When I view it in the gallery I can zoom in a lot and it's still clear but not when I make it a background or upload it. I'm not sure why but any large photo I try to use as my background ends up looking like crap unless I use the ones that came on the device.

Has anyone else been able to solve this issue??