Generate dummy images for testing file upload

Today, I needed to test a file upload mechanism, and needed a bunch of different files, to be able to test that the max file size, max/min file dimensions and image type where correctly checked.

I asked my good friend the command line and came up with the following command to generate the needed files.

$ dd if=/dev/urandom of=1mo.binary count=1024 bs=1024
1024+0 records in
1024+0 records out
1048576 bytes (1,0 MB) copied, 0,0684895 s, 15,3 MB/s
$ ls
total 1,1M
-rw-r--r-- 1 tca tca 1,0M nov.  27 12:00 1mo.binary

This created a 1mo.binary binary file of exactly 1Mo. That can be useful if you simply need to test size limits. But I also needed my files to be valid jpg files. So I used convert.

$ convert -size 640x640 xc:blue 640.jpg
$ ls
total 12K
-rw-r--r-- 1 tca tca 2,7K nov.  27 12:04 640.jpg

This created a valid blue jpg file of 600x600 px. But the file size was way to small, and I simply needed to have bigger filesize but not bigger file dimensions. Best way to do it was to add crappy metadata that will simply adds to the filesize. So I used /dev/urandom again to get random data.

$ cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 1048576 | head -n 1 > 1mo.txt
$ ls
total 1,1M
-rw-r--r-- 1 tca tca 1,1M nov.  27 12:04 1mo.txt
-rw-r--r-- 1 tca tca 2,7K nov.  27 12:04 640.jpg

This generated a 1mo.txt file of random alphanumeric garbage. You can change the fold -w value to increase the size of the generated file. Next step was to feed this value to our jpg file.

$ exiftool 640.jpg -comment\<=1mo.txt
$ ls
total 2,1M
-rw-r--r-- 1 tca tca 1,1M nov.  27 12:04 1mo.txt
-rw-r--r-- 1 tca tca 1,1M nov.  27 12:05 640.jpg

This updated the 640.jpg file by adding the content of 1mo.txt into the comment metadata. You need to use the <= syntax to feed it the content of the file because your shell might not like having a 1Mo argument. Also, you need to escape the < or your shell will try to interpret it.

Now you're ready to generate jpg files of any dimensions and any filesize.

Tags : #convert, #exiftool, #upload

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