Translation:Digital photos are large files.
The plural indefinite article "des" becomes "de" in front of an adjective.
- des fichiers lourds
- de gros fichiers.
The literal translation "Digital photos HAVE large files is much nearer to the truth but is rejected!
photos are not files - they are images. The file contents can be used by suitable software to generate the image but the file itself is a series of binary digits. So the correct translation should be digital photos require large files or similar.
Duo accepts: "Digital photos make big files." But then I wonder why not "font" instead of "sont"?
you're trying to be pedantic yet you can't be more wrong. all digital files have extensions and that in essence distinguishes the file type. so yes a file can be an 'image file'. therefore the sentence given is perfectly fine.