Representation of what I believe is a chasseur of the 1er batallion étranger (not to be confused with the 1er régiment étranger), till now referred to as a member of the 1er régiment d'infanterie légère:
As far as I know, the image was first published in Pierre Charrié, Lettres de Guerres 1792-1815, p. 187, who assumed that this soldier was a musician of the "1er régiment de chasseur d'infanterie légère" [sic], then by Frédéric Berjaud in his article on "Le 1er Régiment d'Infanterie légère, 1796-1815" (Fig. 21e):
Definitely, this is not a musician, as Frédéric Berjaud correctly states (caption to figure 21e: "La légende du document indique qu'il s'agit d'un Musicien; mais il y a semble t'il erreur..."; however, as far as I can see, it is not the "légende du document" which says so, but just what Pierre Charrié mistakenly suspected).
The pompom with houpette, epaulettes and saber knot show that he must be a chasseur, as Berjaud correctly says (tréfoils instead of epaulettes would have been expected if it were a musician's uniform, anyway).
However, like Charrié, Berjaud is of the opinion that he is wearing (a variant of) the uniform of the 1er régiment d'infanterie légère. I don’t think so. Rather, I think that he must be a chasseur of the 1er bataillon étranger stationed at Den Helder/Texel island around 1811/12.
First, a few words about the letter that was embellished by this illustration and can be found in Charrié's book as well (p. 186). It is dated November 5, 1812 and was written at Texel, in Dutch. Unfortunately, I don't speak Dutch, the handwriting is awful, and the spelling seems to be pretty bad. Still, I may have been able to extract some relevant information from the text written along the left edge. Such things as:
"...in het ylandt Tessel hollant[?]...", "pier morel Sasuer Vrans Andre[?] Eerste battelion onder de Vyfde compeine[?]"
...or so. As mentioned, that's just an attempt at grasping some relevant information:
"...on the island of Texel, Holland [if it actually reads "hollant"; might also refer to "battelion"?]", "Pier Morel [Pier(r/e?)Morel(l)], Chasseur, French [if this actually reads "Vrans"; could also refer to "battelion"?], Andre [I may have totally misread this word; no idea; maybe "foreign-"?], 1st battalion, in the fifth company[?]"
Well, that's just a guess. Perhaps some competent friendly Dutch native speaker could help and decipher what exactly is written in this letter (and whether the author was male or female?):
Some general remarks on the picture:
There is a chasseur wearing a light infantry style uniform, accompanied by two ladies. I recognize "Trinje Morell" - wife? sister? else? - , and "Lien de Brand" - sister-in-law? else? I don't know if I have read the names correctly. Perhaps, more is revealed about their exact relationship in the letter itself? "Trinje Morell" holds a letter in her right. Maybe the present letter? Is she the recipient or the writer of the letter? Again, a Dutch native speaker may be able to settle this. In the background, some warships, probably of the Den Helder/Texel squadron.
Now, for the soldier's uniform:
There is a reconstruction by Ernest Fort showing a soldier of the 3e bataillon étranger in 1811, based on an inspection report dated 19 December 1810:
Comparing this reconstructed uniform with the image of the letter, we notice that the reconstruction appears to have turned out surprisingly correct, on the whole. Basically, it is the same uniform, but the one of the letter with more features distinguishing an elite light infantry chasseur: green and red pompom with green houpette, green epaulettes with yellow attente and bezel instead of shoulder straps, sabre briquet with green saber knot. The habit has pointed lapels whose tops appear to be rounded, according to the letter illustration, and square cuffs and cuff flaps in both cases. The coat and facing colours are the same in both cases. The shako has chin scales in the case of the letter illustration. Instead of Fort's eagle, a number "1" or "I" within a horn on the shako plate is indicating the number of the battalion. Another differing feature are the half gaiters which in the case of the letter illustration are pointed and reaching to mid-calf only (the gaiter buttons are clearly visible, though). Whether Fort's reconstruction represents some actual differences in the uniforms of the 1er and 3e batallions étrangers (or between different branches within the battalions: "fusiliers", no sabre briquet, versus "chasseurs", with sabre briquet?), or whether he was just mistaken regarding some features not or not exactly described in the report, I cannot tell.