This post was co-written with Solo PR community specialist Jennifer Spivak.

Between Pinterest’s rise to fame as the third most popular social network in the U.S. by some accounts and Facebook’s $1 billion acquisition of the mobile photo sharing app Instagram – a company that was just two years old – it’s easy to see that if content is still king, visual content rules the social web in 2012. There’s been a lot of interesting discussion about the trend toward more visual content/learning, and strong visuals are clearly here to stay as an increasingly important element in any PR program.

As solo PR pros with budgets that are often more limited, the ability to find free, high-quality images online for use in blog posts, presentations, and on social networks – and edit them using free tools –  is now more essential than ever. But don't just search Google Images and copy something from there (this is tantamount to stealing).  There are many resources and tools available for no cost, high quality visuals – our favorites follow.

Free Image Downloads

1. FreeDigitalPhotos.net
Quickly downloading photos from this online database of free images is especially easy since no registration is required. Though each image on this site can be purchased as a higher resolution file, internet-ready images are available for immediate download free of charge, provided you adhere to the site’s Terms of Services and provide attribution to the original photographer. On FreeDigitalPhotos.net, this means inserting a hyperlink to the contributor’s profile page if the image is to be used online, or publishing the following credit along with photos used in printed materials: “Image: [NAME] / FreeDigitalPhotos.net”

2. StockFreeImages.com
Though there’s one extra step to using this site in that you have to register first, this online collection of 431,000+ images operates similarly to FreeDigitalPhotos.net: give proper credit to the author, and use of the image is entirely free. On this site, an HTML credit line is automatically generated upon download that looks something like this: “© [NAME] | <a href=”http://www.stockfreeimages.com/”>Stock Free Images</a>”

3. Stock.xchng
Like the resource listed above, users must register and sign in to access the 350,000+ quality stock photos by more than 30,000 photographers found on this site. All images here are entirely free as long as users stick to the rules found in their Image License Agreement, which specifies where/when you can and can't use an image. There's also an option to contact the photographer if you'd like to use their image for purposes other than those allowed in the agreement.

4. Compfight
It's a common misconception that all images on Flickr are freely available for use. Not true! Compfight is a search tool that allows you to filter Flickr images and view only those available through Creative Commons or for Commercial use (depending on your needs).

On Flickr, the “license” terms for each image are in the right sidebar – click the words “some rights reserved” to see the details. Some images are shared with permission to “remix” (which means you can crop it, or add a title on top of it, for example), while some are not. Most “some rights reserved” images ask for attribution.

5. iStockphoto’s Free Photo of the Week
Every week this site posts a new image, accessible from its home page, that it makes available for free (to give users a reason to keep coming back). You may not have use for the image today, but it never hurts to download these into a folder and save for the future.

Of course, sometimes paying a relatively small fee (usually around $2, depending on size) to a site like iStockphoto.com or Shutterstock for the perfect image is worth it. But if you’re just looking to jazz up a boring PowerPoint or illustrate a blog post, the sites above can often fill the bill.

Free Photo Editing

Our long-time favorite editing tool, Picnik, was shuttered by acquiring company Google in April (some of its features have been incorporated into Google+).   We’re currently trying out the following:.

1. PicMonkey
PicMonkey is certainly an appropriate Picnik replacement, as the service was actually started by former Picnik engineers. PicMonkey is free and doesn’t require registration (checkout the rather advanced human touchup tools – it’s hard to beat a good teeth whitener and wrinkle remover!).

2. BeFunky
Another photo editing site where registration isn’t required, BeFunky comes with all of the basics like the ability to fix red-eye or bad lighting, but also insists that it has “more effects than any other photo editor, and features you won't find anywhere else.”

3. Aviary
Aviary is a suite of powerful creative applications that you can use right in your web browser. This site allows for photo editing with tools like the Image Editor, Screen Capture, Vector Editor, Image Markup, and more

Do you have any favorite resources or tools we missed? Let us know in the comments!

Image: Idea go / FreeDigitalPhotos.net