Many people would love to edit their own photo’s, re-size them to give them to someone to put on a website or to put them up themselves. However most people don’t want to spend a few hundred dollars on software that can do this efficiently(re-sizing in windows paint isn’t efficient or effective).
There are a few different options, windows and mac both offer tools that you can download (windows live) that have some editing tools built in to make updates. However if your looking for an easy solution and have high speed internet there are some great online options.
You can upload or photo’s edit and re-size with lots of different options, you can then embed them from thier on to other websites or you can even save them to your local computer and upload them to where you would like to have them.
Another great online tool to upload your photo’s and edit them with many options. I’m not sure if you can resave them directly with flickr but if not just right click on your edited photo and click ” save as ” if your using fire fox ” save image as” and you can save it to your local machine. That way you have a copy on your computer for back up or to share on other websites without having to depend on Flickr.
Now with all of the tools mentioned you will be able to do many simple edits but for cleaning up images to make really big changes I would recommend looking into the actual Photoshop Software, with all of the options with it you will be able to create almost anything you can imagine ( with a bit of training 
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