Image scaling changes

Question

Before I started here, the team was using FrameMaker 8 and migrating to FM 10. During the migration, we noticed that images in the documents we opened, converting them to FM10, had their image scaling data changed.
Typically, we acquire screen shots using the highest resolution screen supported - mine is currently set at 1440 x 900. We scale the images to a width of 510 pixels (optimally) but no more than 600 pixels in our screen capture utility. We save the screen shots as Grayscale JPEGs. This process has, historically, provided images that fit our text column flow perfectly.
In previous versions of FM, the images imported by reference appeared as 100% scaling in the FM image properties. Now, they appear as 75% scaling. We're wondering why and if there is any effects we need to be aware of in terms of PDF and HTML Help file sizes.
While testing the import process, looking to see if the FM scaling data affected the image size, we saw that the pixel dimensions given by SnagIt varied wildly from the pixel dimensions given by FM. For example, the SnagIt dimensions for one image indicated it was 505x493 pixels whereas FM gave the dimensions of the source file as 507x315 pixels. Both are, as far as I know, giving me the source file dimensions but they are different.
We might not have noticed this, the images looked okay, but we were carefully going through the transition to FM10 and looking at every detail.
Question: why is FM10 auto-scaling the images to 75%?
Question: does this scaling do anything to our output that we need to be aware of?
Question: why do we get two different dimension data from the two software packages?
Thanks,
Wanda

Answer 1

We  save the screen shots as Grayscale JPEGs.
Are the screen images contone (e.g. real-world photos, CGI imagery),
or flat (e.g. dialogs, line art)? JPEG uses curve-matching compression,
which is great for tones that vary smoothly, but introduces nasty ringing
edge artifacts on sharp edges of flat tones.
TIF(zip), uses repeat-count compression, and is both non-destructive to flat
tone images, and often compresses them more efficiently. We use EPS
for the import format (no compression) and let Distiller or Acrobat post
determine the compression to use.
This process has,  historically, provided images that fit our text column
flow perfectly.In  previous versions of FM, ...
What is the target delivery format?
... the images imported by reference appeared as  100% scaling in
the FM image properties. Now, they appear as 75%  scaling.
In case you want to try it, I have never seen imported EPS objects
change size when migrating a document to a later rev of FM.
We import using 96 dpi.
If the target is PC screen display at 100% page size, that's probably a
decent target. PC screen resolutions today probably range from 80 to
110 dpi, and I'd guess that 96 is very close to the sweet spot.
We use (and I favor) bringing in all contone content at 200 dpi or
higher. We bring bitmap (bi-level line art) in at 600. But then our
target media is 600 dpi B&W bitmap on paper. However, we like
to give web readers of the PDFs reasonable detail in images.
Apple's "Retina" crusade is trying to move the industry to 300 dpi
displays. I'd be happy with 200.