Screen Capture Formatting Issues

If you are just making stills from the videos without any other changes, you don't a project, anyway.

Select the desired frame and share right from the browser.

OR BETTER YET: do not use Final Cut Pro for this.

Open the clips in turn in Quicktime Player, place the playhead on the image you want, press Command-C to Copy; switch to Preview, press Command-N for "New from Clipboard". Save in the desired format.

It sounds as though there is a problem with your video footage.

What are its specifications and also the project specs?

If your footage is in the traditional landscape orientation you should have no problems with the exported still.

Your project is 1920x1080, which the usual HD resolution. It has a 16:9 aspect ratio.

What is inside the project? What are the media dimensions? If the media does not match the project aspectio, then it will either have "black bars" on top and bottom, or left and right; you can fix this, for example, by showing "Fill" under "Spatial Conform" in the Video Inspector.

Unfortunately your last screenshot has the Inspector's audio pane. Show us the Info pane instead.

The export function says this is 3328x2496 but the project in the second image indicates that's it's vertical video at 1080x1920. Not sure what's going on here or what you've done to reach this stage.

As Tom pointed out, the project you are showing is 1080x1920 (I mistakenly wrote 1920x1080).

Your clips seem to be in an unusual size of 3328x2496.

The clips in the timeline will show a big letterbox (black bars on the top and bottom).

Exporting from that project, you would end up with a 1080x1920 tiff file with big letterboxing.

But in the other screenshots, you are sharing from the browser, not the timeline.

Notice how in your last screenshot, the browser has focus and a browser clip is active (see the yellow border).

Also, note that the share window mentions the name of the clip, and not the project.

Finally, sharing this way will not get you any black bars, since you will be exporting in the original size and aspect ration of your clip.

Why you have a vertical project for that media, I don't know, but that is easy to fix.

Select the project, open the Inspector, click Modify, choose Custom and enter the size matching your clips.

If the project is all stills, I would suggest that you use the original images rather than going through Fcp, unless there's an effect being applied that cannot be reproduced in a graphics application. For print or sharing, the original images will give been resolution.

How exactly are you capturing the images? Are you using Share> Save Current Frame?