Draw a rectangle and a text in it using PIL

You can do it without composite()

from PIL import Image, ImageFont, ImageDraw, ImageEnhance

source_img = Image.open(file_name).convert("RGBA")

draw = ImageDraw.Draw(source_img)
draw.rectangle(((0, 00), (100, 100)), fill="black")
draw.text((20, 70), "something123", font=ImageFont.truetype("font_path123"))

source_img.save(out_file, "JPEG")

You can create empty image with size of button and put text on it and later put this image on source_img. This way long text will be cut to size of button.

from PIL import Image, ImageFont, ImageDraw, ImageEnhance

source_img = Image.open("source.jpg").convert("RGBA")

# create image with size (100,100) and black background
button_img = Image.new('RGBA', (100,100), "black")

# put text on image
button_draw = ImageDraw.Draw(button_img)
button_draw.text((20, 70), "very loooooooooooooooooong text", font=ImageFont.truetype("arial"))

# put button on source image in position (0, 0)
source_img.paste(button_img, (0, 0))

# save in new file
source_img.save("output.jpg", "JPEG")

EDIT: I use ImageFont.getsize(text) to get text size and create button with correct size.

from PIL import Image, ImageFont, ImageDraw, ImageEnhance

source_img = Image.open("input.jpg").convert("RGBA")


font = ImageFont.truetype("arial")

text = "very loooooooooooooooooong text"

# get text size
text_size = font.getsize(text)

# set button size + 10px margins
button_size = (text_size[0]+20, text_size[1]+20)

# create image with correct size and black background
button_img = Image.new('RGBA', button_size, "black")

# put text on button with 10px margins
button_draw = ImageDraw.Draw(button_img)
button_draw.text((10, 10), text, font=font)

# put button on source image in position (0, 0)
source_img.paste(button_img, (0, 0))

# save in new file
source_img.save("output.jpg", "JPEG")