Do use a photo editing program
Many of you are saying, I'm not a great photographer. What can I do? Can I succeed on Pinterest? Yes! Consider trying a free photo editing program online like Pic Monkey or Canva. Both have free versions that you can use improve the look of your images. If you have a little bit more money to spend, I love Adobe Photoshop or Adobe Photoshop Elements. I'd recommend Elements for a beginner because it is the less expensive and more user friendly of the two programs.
If you want to rework posts that don't contain vertical images to make them ready for Pinterest, consider creating collages or adding text descriptions. Both are great ways to make your existing images work for Pinterest.
A lot of my oldest posts were created before Pinterest came along and before I knew much about photography. (I still have a lot to learn!) All of my photos used to be tiny and square. Ugh! I've gradually gone back and fixed the images in many of my old posts to make them more Pinterest friendly. Here are a few examples of how to transform square or horizontal images for better traction on Pinterest:
Before (Visit the Post - How to Build a Watering Can)
I cropped the image, brightened it up, and added a text overlay.
Before (Visit the Post - Felt Food Sandwiches)
I removed the huge watermark, brightened the image, removed shadows, changed the cropping angle, and combined the image with other photos from the post to create a collage. I also added text overlays.
Before (Visit the Post - Halloween Finger Puppets)
I brightened the image, added more negative space between the hand and the overlay, and added another image to make the pin extra long for Pinterest.