GIMP has a useful tool to capture a screen image so that you can edit it or just save it as a JPEG (xxx.JPG) file on your computer. Have the image you want to capture in a separate window where you can drag the cursor into the window. Then open the GIMP application and click on the pulldown tab FILE.
Click on CREATE and on the submenu click on SCREEN IMAGE.
To save as a JPEG file, move your mouse over the FILE tab, click SAVE and select the file format, enter the file name and locate the folder you wish to receive the file in the submenu. Then save the file. Bingo!