For short screencast videos (1 & 2), I prefer using GIF animation over Flash because GIFs can be inserted just like JPEGs and are more likely to get noticed by people who read content inside news readers.
Now creating a brand new GIF slideshow from photographs and screenshots is easy but to edit GIFs, you would need GIF Make.
GIF Make is a no-frills but useful web application that splits a GIF image into individual frames that combined make up the entire animation.
You can then delete any of these frames, replace a frame with another picture or even change the duration for which that frame gets displayed in the final movie.
GIF Make can also help you combine two or more animated GIFs into a single file - just load them in sequence.
Related: Extract Image Frames from GIF