Louis Icart is probably best-known for his work in etchings.
Etchings are made in a multi-step process that starts with a sketch. This sketch is then used as a guide to make a plate which will be the source for multiple copies of this image. The first etchings in a group tend to have finer colors and line detail.
In the large majority of cases, Icart only made 500 etchings per print, so it is accepted to call each etching an "original" since there are so few, and productions of prints differ from beginning to end.