I have both a video clip and still images (for a time lapse sequence) shot from the same angle on a tripod. I'd like to dissolve from the video clip into the time lapse sequence as smoothly as possible... so I'm looking for a way to align or crop the time lapse still images to match the video frame as closely as possible.
But do this first. Take still frames from the footage and save them out. Use photoshop or GIMP To analyze both sets of stills , the frame shots and your photos. Look at levels,and grain, Look at the color and channel histograms and match them , unless you do not care if they blend or have and artistic purpose in mind. Take notes of the levels and color, Gamma etc for the match.
If you are an experienced user you can probably do this in the effects controls with your effects plug ins.
Overlay your photos where needed in the timeline.
Adjust your motion controls for the photo layer to match scale and position. You can adjust opacity to see through your layer to get and exact scale and position match. Leaving the photo aspect as shot you can do magic tricks with motion effects. But an exact match should be easy as long as you shot footage and photos with square pixels.
You can also fine tune and adjust colors, levels and match grain in the effects controls.
You can then restore or blend your photo overlay opacity along the timeline. If you need guidance there just ask.
Your effects control basics of position, scale and opacity are very basic level PrPro tools. So familiarize yourself with them . It gets to be a first line go-to for lots of special video effects.
If you have After Effects it makes all of this more precise and also easier if you learn the interface.