Am I breaking any law by digitalizing a curve from a plot on a scientific Journal if I cite the source and I mention the tool I used? Am I breaking any law or etiquette/guideline by:

digitalizing a curve from a plot published on a scientific Journal
using the data (the curve) on a paper I am submitting to another journal. I to compare the curve to my curve in my plot, I make sure I cite it and I say the tool I used to extract the data.

EDIT: I am speaking about using a digitizer (like a program that given a published figure with a curve and the coordinate axis it gets you the data).
It is a general question, since many journals are international, publisher might be  from UK, author from USA and I (the one trying to digitize the data) could be from New Zealand.
At least in the USA this is explicitly OK, so long as by 'digitize' you mean 'find a mathematical expression of the nature of the curve'. As long as you do not use the original image, you can even reproduce the curve from the that information. Data, as in observations about the natural world, cannot be copyrighted.
If you are 'digitizing' in the sense of creating a digital image, most journals will request you obtain permission to reproduce the image you found in the original article. &quot;Creative and expressive' mediums, such as data visualization, are fully copyrightable.
You also might consider reaching out to the authors anyway, to get their own data used to produce the curve. Reviewers and readers will prefer this, as it ensures the description of the curve is accurate. Almost any author should be amenable to this.