You can provide data in GET parameter: https://barcode.edv-schmittner.de/barcode.php?f=png&s=code-128&d=DATEN
Options:
f - Format. One of:
png
gif
jpeg
svg
s - Symbology (type of barcode). One of:
upc-a code-39 qr dmtx
upc-e code-39-ascii qr-l dmtx-s
ean-8 code-93 qr-m dmtx-r
ean-13 code-93-ascii qr-q gs1-dmtx
ean-13-pad code-128 qr-h gs1-dmtx-s
ean-13-nopad codabar gs1-dmtx-r
ean-128 itf
d - Data. For UPC or EAN, use * for missing digit. For Codabar, use ABCD or ENT* for start and stop characters. For QR, encode in Shift-JIS for kanji mode.
w - Width of image. Overrides sf or sx.
h - Height of image. Overrides sf or sy.
sf - Scale factor. Default is 1 for linear barcodes or 4 for matrix barcodes.
sx - Horizontal scale factor. Overrides sf.
sy - Vertical scale factor. Overrides sf.
p - Padding. Default is 10 for linear barcodes or 0 for matrix barcodes.
pv - Top and bottom padding. Default is value of p.
ph - Left and right padding. Default is value of p.
pt - Top padding. Default is value of pv.
pl - Left padding. Default is value of ph.
pr - Right padding. Default is value of ph.
pb - Bottom padding. Default is value of pv.
bc - Background color in #RRGGBB format.
cs - Color of spaces in #RRGGBB format.
cm - Color of modules in #RRGGBB format.
tc - Text color in #RRGGBB format. Applies to linear barcodes only.
tf - Text font for SVG output. Default is monospace. Applies to linear barcodes only.
ts - Text size. For SVG output, this is in points and the default is 10. For PNG, GIF, or JPEG output, this is the GD library built-in font number from 1 to 5 and the default is 1. Applies to linear barcodes only.
th - Distance from text baseline to bottom of modules. Default is 10. Applies to linear barcodes only.
ms - Module shape. One of: s for square, r for round, or x for X-shaped. Default is s. Applies to matrix barcodes only.
md - Module density. A number between 0 and 1. Default is 1. Applies to matrix barcodes only.
wq - Width of quiet area units. Default is 1. Use 0 to suppress quiet area.
wm - Width of narrow modules and spaces. Default is 1.
ww - Width of wide modules and spaces. Applies to Code 39, Codabar, and ITF only. Default is 3.
wn - Width of narrow space between characters. Applies to Code 39 and Codabar only. Default is 1.