Use Canvas Size when the task is to add blank space around a Photoshop photo without changing the photo's scale. Image Size and a non-proportional transform can change the picture itself. A border should increase the surrounding area, not widen a person's face. Decide the required margin and its location before changing dimensions.
Record the image area you must preserve
Keep the original and make a working copy. Note the source photo's pixel width and height, and identify a recognizable feature such as the distance between the eyes or the width of a product label. Those landmarks help detect an unintended stretch that a larger overall file size can conceal.
Separate the desired canvas dimensions from the desired image dimensions. An album page can be larger than its photograph because it contains a border or caption area. It does not follow that the photograph needs to be resampled to fill the page. If a layout needs both a larger page and a smaller photo, treat those as two deliberate operations.
Add space with an explicit anchor
In desktop Photoshop, choose Image > Canvas Size. Set the required width and height, checking the unit and whether the entered values are absolute or relative. Use the anchor control to determine where existing content stays while space is added. A centered border and a larger lower caption area require different placement decisions.
Choose an appropriate extension appearance for the document's layer state. An ordinary background color and transparent added space are different deliverables. Canvas expansion does not invent scene detail; if the added region needs matching walls or landscape, that is a separate content-creation task rather than a white-margin operation.
Compare geometry on a copy
This is a reproducible test plan, not a tested album file. Add a small border on a duplicate while leaving the photo layer's transform unchanged. Measure the original image area again and compare the chosen landmarks. The full canvas should grow while the photograph's proportions remain the same.
Inspect all four margins at actual pixel size. If space was intended only below the photo, verify that it did not appear above because the anchor was reversed. If the image itself stretched, return to the preserved copy and inspect which command or transform changed it. Do not compensate by distorting the face in the opposite direction.
Acceptance before card or album output
Accept when the specified blank area exists, the original photograph retains its geometry, and the final layout fits the planned card or page. Check any separately placed text for readability and keep it editable. A correct border does not certify print scale, bleed or printer expansion; those need their own delivery checks.
Save the master and reopen the exported image to verify its actual dimensions and margins. Imagild can create or edit the photo material. The precise canvas and anchor controls described here belong to external Photoshop, so do not interpret the guide as a promise of identical layout controls in Imagild.