Watermark an image

First, create a blank image that will serve as a canvas for the watermark:

convert -size 900x15 xc:white filename.ext

Then, print a custom text to the previously created blank image:

composite label:'label-here' input.ext output.ext

Finally, apply (append) the watermark as desired.

To a single image:

convert input.ext watermark.ext -append output.ext

To a series of images:

Use a for loop:

for img in image-name-**.ext; do
  convert $img watermark.ext -append $img
done

Where img is the chosen attribute name, and * is a wildcard character used to match files with the same naming pattern.

Notes:

• Being $img set as input and output, the original images will be overwritten by the watermarked ones.
• This loop uses the bash syntax
• The loop can also be used in single-line form for img in image-name-**.ext; do convert $img watermark.ext -append $img; done

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Crop an image

Use the cli command convert filename.ext -crop 000x000+00+00 croppedfilename.ext, where 000x000 is the desired size of the cropped image and +00+00 specifies the coordinates of the cropping point; note that the offset position of the "-crop" by default is relative to the top-left corner of the image.

Examples:

# Crop an image:
convert input-image.jpg -crop 1488x963+96+29 output-image.jpg

# Crop all the .jpg images in the working directory:
convert *.jpg -crop 1488x963+96+29 *.jpg

# Crop an image relative to its center:
convert input.jpg  -gravity Center -crop 00.00%x000+0+0 output.jpg
# Where 00.00% defines the amount of image width that will be cropped, expressed in percentage

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Resize an image

There are different methods:

By dictating the total desired pixel area count:

convert *.jpg -resize 460800@ *.jpg

Fixed height, proportional width:

convert -resize x480 *.jpg *.jpg

Fixed width, proportional height:

convert -resize 960x *.jpg *.jpg

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Perform batch operations in Imagemagick

Use a for loop, for example:

for file in ./*;
  do convert $file -gravity Center -crop 89.35%x420+0+0 output-dir/`basename $file`;
done

This loop crops files in the current directory and saves the output to a previously created output-dir directory.

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Append images

There are different methods, based on the desidered result:

For merging 2 images into 1:

convert input-1.ext input-2.ext -append output.ext

For batch processing:

convert *.png -append output.png

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