Read the upload instructions before editing
Open the page that will receive your file and check its instructions beside the upload button. Write down the maximum file size, which file formats it accepts, and any required pixel dimensions. These are separate limits. A file can be small enough and still be rejected for being too wide, too short, or saved in an unsupported format. Also check whether the form asks for a single image or accepts a PDF. Making the right type of copy at the start saves time and helps you avoid converting the same file again and again.
Keep an original and a working copy
Make a copy before you crop, resize, or compress. Give it a name that describes its purpose, such as profile-photo-for-upload.jpg. Keep the unedited photo in its original folder so you can start again if the first edit looks soft or cuts out something important. This is especially helpful when the same photo has to go to two websites with different rules. Export both versions from the original when possible. Repeatedly saving one compressed JPEG can make small details harder to see, even if the next version has roughly the same dimensions.
Crop the photo to a square
A 600 by 600 pixel image has equal width and height. Start with a square crop if your original is rectangular. In your editor choose a 1:1 crop, move the selection until the important part of the photo is inside it, and keep enough space around the edges. Save a separate copy when you finish. This gives you a square to resize and keeps faces and objects in proportion. Stretching a rectangular image directly into a square can distort the subject.
Resize the square to 600 pixels
Open the cropped copy in a tool that shows size in pixels. In Preview on a Mac, use Tools and Adjust Size. In Paint on Windows, open the Resize controls and choose pixels. With the aspect ratio locked, enter 600 for the width and check that the height also reads 600. Export a copy in the format the destination accepts. Reopen it and check the file information. A document setting such as 300 DPI by itself does not set the dimensions to 600 pixels.
Meet the size limit without changing the dimensions
If a form also requires a small file, resize first and then adjust JPEG quality while keeping the canvas at 600 by 600. Check both values again after saving. The general compressor linked below can reduce dimensions when needed, so use it only if the destination allows the resulting dimensions. For official photos, follow the receiving agency’s rules on framing and edits. A square image can still fail an official photo check if the face, background, or crop is wrong.
Review the result at full size
Open the finished file by itself. Zoom in on the details the recipient needs, including text, faces, or edges that show the full document. A thumbnail can hide blur and compression artifacts. If you see smearing around letters or blocks in smooth areas, go back to the original and adjust one setting at a time. Crop unused edges if the destination allows it, or try a slightly higher quality setting and reduce the dimensions only within the form’s limits. Compare the exported file to the original before you decide which version to submit.
Check the file and try the upload again
Use your file manager or editor to check the finished copy’s file type, dimensions, and size. The actual file selected in the form matters more than the settings you remember choosing. For example, a photo editor may append a suffix to the new export while leaving the original in the same folder. Read the filename in the file picker before you submit. If the upload is still rejected, note the exact message and compare it with the form’s rules. A generic message may cover several issues, including an unsupported extension or too many attachments.
If you need a second version
A website profile, a job application, and a document portal may all ask for different copies of the same photo. Keep one master image and name each output for its destination. Include the dimensions or size limit in the filename if that helps you tell the copies apart. When a form accepts JPEG and the limit is 100 KB, the linked tool can create a smaller copy in your browser. Check the output dimensions before using it on a form with a fixed pixel size. For an upload that requires a transparent background, export in a format that supports it.