Photoshop Elements is available on most University of Illinois library computers. It is a version of the powerful Photoshop CS6 software and will be able to make just about any change to a photograph that you need. Though it does not have all the tools and functionality of CS6, Elements is generally easier to use for someone unfamiliar with the program or someone wanting to do minimal editing. Elements is also cheaper to purchase. Photoshop Express Editor is Adobe's free online image editor, not to be confused with Photoshop Express, which is an app for iOS, Window, or Android.
For tutorials on using Photoshop, check out the Scholarly Common's Library Guide about Adobe Photoshop CS6 for the beginner user or Lynda.com's Photoshop tutorial, which is available with University of Illinois log in credentials
Students, faculty and staff can purchase Photoshop through the University of Illinois Webstore. Both Photoshop CS6 and Photoshop Elements are available for Mac and PC at a discounted price. Upgrades from previous versions of both are also available.
There are a lot of free image editors out there; they vary in degrees of difficulty, but all are free to download and use. Some popular ones include:
From Wikipedia: "Optical character recognition, usually abbreviated to OCR, is the mechanical or electronic translation of images of handwritten, typewritten or printed text (usually captured by a scanner) into machine-editable text."
If you have photographs of printed or typed sources, OCR may save you from having to re-type information, and makes files full-text searchable. Note: OCR works best when the image is clear, not crooked, and there are no obstructions. This still does not ensure that a software will properly be able to perform the OCR -- it may still copy as a bunch of gibberish. However, it is potentially a useful tool in your research.
You will need Adobe Acrobat Professional or Standard, available on many University of Illinois library machines, to convert your images to PDF files. Both Adobe Professional and Standard are also available for purchase at the University of Illinois webstore or trial download from the Adobe website.
For more extensive OCR capability, you can use ABBYY Finereader, which is available on all Scholarly Commons computers.