If not maybe this will help.
Converting screenshots or other pictures to jpg’s or changing the DPI is so easy using a program called Paint.net.
Thought I’d share with y’all my steps.
For screenshots, I use a screen recorder called Icecream Apps. It’s a FREE download and super easy to use.
Select the picture or area of your computer screen you want to copy and select screenshot. Save. The program saves it as a .png. This is where I reach for one of my favorite programs, Paint.net.
This is where I reach for one of my favorite programs, Paint.net.
In your file folder, 
find the picture and right click to “open with” Paint.net. Once the picture opens, do a “save as” a Jpeg.
Next, you can manipulate the size and DPI of the picture.
Click on “Image” in the drop down menu. Select “Resize”
Jean's Writing 
I just checked this out. Mac is not supported. Hope you did well at AuthorCon. I’d like to hear your thoughts. Will you go again next year?
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Yes, it was fun. Met some really nice authors. Not sure about next year. I’d like to see some things done a little differently. But being new to this type of venue, not sure what to expect.
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One thing that some people aren’t aware of is “inches” and “centimeters” aren’t used on a computer screen, whether it be a PC, tablet, or iPhone. In the computer world, pixels/tiles are used. Approximately 325px (pixels) equals 5 inches or the width of a business card. Although, for picture quality, png is preferred, when trying to get the weight of the picture down so it loads fast on a screen, jpg and gif is a better way to go. Gif is better for illustrations, where jpg is better for photos. So far, the only 2 programs I’m sure about that have the tool to lessen the weight are PaintShop Pro and Photoshop. There’s probability other programs out there but I don’t know what they are.
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Thanks for the tip! You’re so right a lot of us are familiar with how px work. So much to learn and so little daylight hours. LOL
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Turns out Paint.net doesn’t yet have a Mac version (if I’m wrong, I hope someone will provide a link). Mac users can capture screen shots using the Grab utility or COMMAND + SHIFT + 3 for the whole screen or COMMAND + SHIFT + 4 for a selection. You can open your screen shots in Mac’s Preview for resizing and changes in resolution. Preview, in fact, has a screen shot option as well as a variety of “markup tools” such as the addition of text. I downloaded GIMP because I wanted more ability to work in layers, but to add to Jean’s great advice here, for many uses, if you’re on a Mac, Preview works fine.
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I do hope you’ll check out Sumo Paint for layers. I think you’ll be floored after struggling with Gimp. Thanks for all the info on Mac, as a Windows user I know little to nothing about Macs.
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