Moving photos from computer to iPhone?

Hi I'm totally new here. I wanted to find out how to move a j.peg photo from my laptop to my iphone5S to post to Instagram without loosing any resolution and keeping the images sharp. I have been using Dropbox and it works ok for close ups and macros but when I try to do a landscape photo that is in perfect resolution on my computer screen, the resolution is horrible on the phone. Also I use some editing apps as well as editing on Instagram and I also use the ezy watermark app to put my name in, this makes my landscape photos loose even more resolution before actually posting to Instagram.
There must be a way to do this? I see photographers post beautiful landscape photos to Instagram that have sharp resolution.
Thanks for any help and insight.

For some reason Apple likes to reduce the resolution of photos when they get transferred.

The best way to add photos to an iDevice is to keep them in a folder on your computer and then sync the images in that folder over to the iPhone using iTunes. It's a little clumsy, but that way they maintain their full resolution. This link explains how to do it: http://support.apple.c​om/en-ca/HT201313

Thanks for the link Jim !

What laptop do you use? I usually use the AirDrop feature to transfer photos from my MacBook Pro to iPhone. I think this feature is only available in the latest OS X and iOS.

You can also email to yourself.

There are also several free photo transfer apps for your iPhone you can get from the app store. They work equally well.

Any of these methods is more convenient than sync thru iTunes.

-alex

On a Mac you can just use AirDrop, or you can use a photo transfer app. I quite like this one:
Photo Transfer App - Easily copy, share and backup pictures and videos over wifi between devices and computer by ERCLab, LLC
https://appsto.re/il/S​Q8Wv.i

Another option on a Win PC is to install a free syncios, which is very good:
Syncios.com