White lines in scanned photo image?

As Thomas has said you can do it in Photoshop, but you can also do a Fourier Transform in free software, and use the same technique in GIMP http://www.gimp.org - and the free plugiin G'MIC http://gmic.sourceforge.net/ which contains the fourier transform filter required. So, no need to buy anything!

Once you have installed GIMP and the G'MIC plug-in, first open an image and right click the layer in the layers dialog and choose the option to remove the alpha channel (the fourier transform won't work unless you do that), then to engage the filter click Filters > G'MIC > Spectral Filters > Fourier Transform - set the transform option in the filter to "direct". As per the Photoshop tutorials Thomas linked to, edit the white spots out by painting over them, then finish by running the filter again, but this time set the transform option to "inverse".

By the way, using that technique won't totally remove the pattern, however it will greatly reduce it. You can use the same techniques for any repeating pattern, such as half tone dots on a scan, or even TV scan lines, as long as it's a repeating pattern, it can be removed.

Here's a screen shot using Fourier Transform in GIMP+G'MIC with example edit: http://i.imgur.com/4yg36ix.jpg

There are a couple of options. Using Photoshop, you can use what is called an FFT filter. Here are a couple of instructional videos from YouTube about using an FFT filter:

https://www.youtube.com/watch?v=pC9W-a-aPyg

https://www.youtube.com/watch?v=yyox358zIRw

You would need to have Photoshop and then download or purchase the FFT filter.

There are many amazing tricks that can make your photo look better. Photoshop is an amazing photo editing tool if you want to make your picture beautiful. If you want to learn tricks for photoshop you can visit the site given below.

Indeed that filter might help, but why are there lines on the scan in the first place? Maybe a problem in the scanner?

If you have a good DSLR it might be easier tp photograph the old prints.