Here is the simples way to copy pictures, follow these few steps.
1) Connect your iphone to windows pc.
2) Open itunes.
3) I usually create a new folder on my pc for this purpose, and copy the phones to that folder, meaning the pictures that you want to copy and save on your iphone.
4) Click the little icon on itunes that shows the iphone, so you know you are viewing the iphone, and then go to photos (so you are viewing photos on the iphone)
5) See the option on the right that says "copy photos from"? Click that, click "choose folder" and choose your windows folder where you just put your pictures. Make sure the box above that says sync photos is checked, and down on the bottom click "sync", this will copy all in that folder and you will see them in your iphone photo album. Note that it will show a new folder in your album! They appear there, not in the same location as all your other pictures.