Tools for drawing, for example creating schematics and flow charts
Powerpoint - fairly easy to use, but need to recognize that its
tools are basic and it provides limited control of output image
quality.
Adobe Illustrator - Lots more control and options, which makes
it harder to pick up quickly, but worth the investment. Adobe
licensing is a challenge, check out Purdue's licensing
agreement at Adobe Creative Cloud licensing
to find out how to use the software. Adobe
Illustrator is now part of the Adobe Creative Cloud Suite.
Xfig - available on many Linux/Unix platforms or as
part of their supplemental package system. Cannot confirm
continued support for the package as of 22 Apr 2016.
Most OS have basic photo editors embedded, look on-line for
information about the best to use with your system.
Adobe Photoshop - Lots more options and control, which makes it
harder to get up and running but worth learning if you want to
manipulate photos and similar images. See Adobe Illustrator
(above) for links to the Adobe license.
GIMP (GNU Image Manipulation
Program) - available on many Unix/Linux platforms or can
be installed on most operating systems now, including OS X and
Microsoft Windows. Much of the functionality of Photoshop, but
as a free and open source download.
ImageMagick - available on most Unix/Linux systems, this is
a free and open source image manipulation tool that primarily
works on the command line. Does anything from simple image
format conversions to more complicated command line photo
editing. Works extremely well for automating an image processing
pipeline, where standard changes are applied to a large number
of images.