I'm looking for a good workflow in dealing with a document like this. The files need to be JPEG, but I also can't have any white around the planks. Is there a smart way to select and separate each plank into its own layer, and then export them all at once?
First, to select without white line, the best way here is to select with a rectangle with precision by hand (zoom in). Once a plank is selected,
right clic on it with a select tool active and
Layer via cut.
Do it for each plank (you can move your selection instead of doing a new one since you seems to have multiple same size here.
Once you have each plank on a layer go to
file > export > Layer to file. Here you can select the destination folder, and JPEG with the desired quality.