These are the main ideas to remember regarding using digital images for lectures successfully...
When images are resized appropriately, they will display at their best
Keep a copy of the largest version of an image (maybe a 1-5MB image which is at least 1000 to around 3000 pixels on the longest side, if possible) as an 'original' from which you can make smaller derivatives.
Make smaller derivatives from your larger one based on need (consider whether you are using one, two or three or more images per PPT or Keynote slide).
Look into Using Photoshop for resizing images.
Avoid having to 'drag' the corners of the image once it's uploaded into PPT or Keynote. It's not the end of the world, but it is one cause of blurry projected images
Know that a standard PPT, Keynote or ARTstor OIV slide is 1024x768.
Think of a slide as a 2D layout of a room, and the images are all little rugs used to fill up the room. What size do they each need to be to fill up the room (if that's what you want to do)? View a presentation on our Theory of Using Digital Images. Or download the PDF below. Print it out and keep near you as you get more comfortable working with digital images.
University of Texas at Austin also has a great video explaining this idea.
Start organizing images right away
Start naming images in a way that makes sense to you and
adhere to a naming convention, such as by class. A few recommended
naming conventions which could be used:
largest version of a file with _full as a suffix or full_ as a prefix.
derivatives with suffixes (or prefixes) such as _halfvert, _halfhoriz,
_qtr, _print, or _web
Use a suffix with pixel dimension for
future reference, such as _1024x768
Organize folders on your computer or in other online image
hosting sites by classes or presentations.