You shouldn't need to change any of these.
Instead of deleting old file writing a new one with the same name, just replaces old file's content in-place. This ensures that all hardlinks, aliases, file ownership, permissions, extended file attributes will stay the same.
It's slightly faster not to preserve permissions.
Will write copy of a file with ~ appended to its name. This makes optimization a bit slower and litters your disk with backup files.
Keep it on if you optimize for web. Disable if you have special PNGs with extra metadata.
Removes image metadata, such as color profile, exposure time, GPS coordinates, camera model and name of software used to create the file. Metadata is never removed from JPEG files larger than 1.3MB.
If checked, ImageOptim will try to optimize JPEG files.
If set to 100%, optimization will be lossless.
Anything below 100% will cause lower quality of files if they appear to have been saved with higher quality setting.
If checked, ImageOptim will try to optimize PNG files using PNGOUT.
PNGOUT is not bundled with ImageOptim. It's a great tool, but the author of PNGOUT forbids redistribution of it, so you have to download PNGOUT yourself.
PNGOUT is very effective, but very slow. Use lower level if you're impatient.
PNGOUT may need a lot of time to optimize very large images. This option gracefully interrupts PNGOUT after 1 minute.
If checked, ImageOptim will try to optimize PNG files using AdvPNG tool.
If checked, ImageOptim will try to optimize PNG files using OptiPNG tool.
Number of different setting combinations tested. It rarely makes sense to try them all.
Interlaced images look better when they're loaded partially, but usually interlace makes compression less efficient.
This checkbox has three states: if checked, will force images to be interlaced. When mixed, it will keep file's interlace unchanged, unchecked will remove interlace from files.
If checked, ImageOptim will try to optimize GIF files using Gifsicle.
GIF files will be changed to interlaced or non-interlaced automatically, whichever is smaller. In-file comments will be removed.
Please note that Gifsicle works best with animated GIFs and non-animated GIFs rarely can be optimized
For best compression, you should convert GIF files to PNGs (ImageOptim does not do that automatically).
Jpegrescan is a script based on jpegtran. It uses creates JPEG files with unusual number of progressive scans to achieve better compression, but such files may not be compatible with all browsers.