Image resizing is one of those common tasks that we all need to do, specially if you are posting pictures online. Keeping the files as small as possible but still being large enough to view without losing too much detail will help load the page faster and make for a better online viewing experience. This is specially true for anyone using older and slower hardware which believe it or not, many countries still don't have the fast internet access that some countries do or at least the people don't, so it's good to keep this in mind.
For a long time I really liked Picasa. It was a stand alone program for managing your pictures and making some basic edits. Unfortunately google decided to retire the program in exchange for the cloud version of photos or whatever it is now. I just tested that the other day and it's just as bad as the microsoft one drive look. I personally don't care for either. I like having a stand alone program for these tasks.
In short, I have been using the program that came with my Nikon camera called ViewNX2 which allows me to resize my files. So if your camera came with any software no matter who makes it, you may want to check that first before downloading anything else. I'm guessing many companies have their own programs now. Now, these aren't perfect by any means and if you're a professional, these may not be what you need, but for most basic tasks specially resizing, they may work just fine if your software even has these features.
If your camera didn't have one or you just don't have a way to resize images, I decided to add a few programs here to help with these tasks. I personally like programs that you can install on any system, whether it be windows, mac or linux. This just allows for more flexibility no matter what you use. To me, systems are just a matter of choice and many times budget, so being able to use the same program no matter what you use is definitely a good thing.
XnView is a cross platform so that gets some brownie points there.
Image resizer for windows
FastStone photo resizer - Free for home use
These are just a few of the many, many programs out there but I wanted to touch on this since it's something I find myself doing often in order to make sure that the files I upload don't take forever because many of your phones or cameras will probably be taking some very large pictures if you forget to check them or change your camera settings. It's nice to have a lot of detail, but then you will pay for that when you try to upload or share those pictures. Post the small files, then send/upload the larger files through other methods if you really need that detail.
Update April 3, 2017
ViewNX2 has been updated. I contacted Nikon about it since I was having some issues with the old version. The new version is now called ViewNX-i. Unfortunately they changed the setting to post to say facebook which would export the smaller picture to a web folder. It just wants to connect directly now so I don't get that option which I really liked since I would use that to post the pictures to the blog and not facebook. They still have the export which I have to play with but it just seems to be more work.