Worked usage and result checks

Join images in a deliberate order

Merge Images composes local raster images into one vertical column or horizontal row. It is a sequential image joiner, not a PDF merger, layered design editor or automatic collage layout service. Use it when you need one inspected image containing several owned screenshots or illustrations in a known order. The queue lists the selected files, and the up and down controls change that order. The preview represents the current composition; it does not identify duplicate pages, remove sensitive details or check that each source is appropriate to publish. Keep source files separately if individual images must remain editable after export.

Worked example: two colored cards

Prepare one small red PNG and one blue PNG with different widths and heights. Select them in that intended order, choose a vertical arrangement and set a visible gap. With proportional resizing disabled, the output width is the larger source width and the output height is the sum of both heights plus the gap. The narrower image is left-aligned, leaving background fill in the unused area. Reopen the exported PNG and confirm red appears before blue. Move the second queue entry upward and inspect the reversed result. This tests queue order and canvas extent independently of whether the original pictures happen to look similar.

Proportional resizing has an explicit reference

With automatic resizing enabled, a vertical composition uses the largest source width as its reference and scales each image proportionally to that width. A horizontal composition instead uses the largest source height. The resulting dimensions are rounded to whole pixels, with a minimum of one pixel. This can upscale a smaller source and make it look softer; proportional scaling preserves its aspect ratio but does not create missing detail. With resizing disabled, each image keeps its decoded dimensions and the output still includes the largest cross-axis extent. A later wider or taller image is therefore included rather than cropped to the first file's size.

Spacing, fill and alignment

The gap control supplies zero to one hundred pixels between adjacent images. It does not add an outer border around the entire composition. Choose a six-digit hexadecimal background color to fill the gaps and any unused area beside a smaller image. Transparent source pixels can reveal that fill, and JPEG cannot preserve the result as a transparent layered project. The joiner places images at the start of the cross axis rather than offering a separate center-alignment or crop control. If your destination needs outer padding, captions or a custom grid, prepare those deliberately in an image editor instead of treating the sequential join as a complete page-layout service.

Selection and decoding failures

The queue is bounded to twenty files. Each source must be a nonempty PNG, JPEG or WebP up to ten MiB, within 16,384 pixels on either side and twenty million decoded pixels. File reading and image decoding each have a twenty-second deadline. A mixed selection containing an unsupported or corrupt file fails visibly instead of waiting forever for every file to report a successful load. The selected order is preserved even when individual files decode at different speeds. Selecting a newer group or clearing the queue invalidates an obsolete pending selection, so a late result cannot silently repopulate a cleared workspace.

Output allocation is checked before drawing

The combined canvas must fit 16,384 pixels per side and forty million pixels overall. Several individually acceptable sources can exceed that combined bound after proportional scaling or gap insertion. The page reports the composition limit before allocating the output canvas. Reduce the number of images, choose smaller source files or change the resizing choice, then inspect the new dimensions. A supported output size is still subject to browser memory and encoder availability. The limit does not promise that every device near the boundary will feel instant, and repeatedly retrying a huge composition is less useful than reproducing a problem with two small files.

Download the format you actually need

PNG, JPEG and WebP exports use the current rendered canvas. PNG preserves canvas pixels without JPEG-style loss, while JPEG and WebP can change file size and compression behavior. The selected format must be produced by the browser encoder; a mismatched fallback is reported rather than downloaded under the wrong extension. The export is one flattened raster image and does not retain editable source layers, original metadata or each file's compression bytes. Open the saved result in a separate viewer and inspect its actual type, dimensions, first image, last image and gap color before replacing a maintained document or publishing it.

Processing and queue retention

Reading, decoding, compositing and exporting are local operations without a merge-processing API request. Normal site assets and services follow the Privacy Policy. The queue is in-memory workspace state, not a cloud project store or a promise that a refresh will restore your selected files. Clear Queue removes the current composition state; it does not remove originals, prior downloads or copies uploaded elsewhere. Reordering uses the visible arrow controls rather than drag-to-reorder behavior. If a file contains private material, inspect every source and the complete merged image before copying the output into a ticket, presentation or shared message.

Diagnose the stage that failed

If selection fails, test the suspect file alone in a separate image viewer and export a smaller ordinary PNG before retrying. If rendering fails, inspect the combined dimensions and background color. If the preview looks cropped, compare resizing enabled and disabled with two visibly different card widths and verify the output extent. If the order is wrong, use the queue arrows and compare the first and last source again. If export fails, choose PNG and read the visible message rather than assuming the preview was saved. This staged rehearsal distinguishes source decoding, geometry, ordering and file encoding instead of treating all four as one undifferentiated merge operation.

Merge Images Online — Join & Combine Photos Sequentially