Why this tool defaults to the largest accepted size
IIT JAM’s brochure gives a range for the photo, not a single fixed size: anywhere from 240 × 320 up to 480 × 640 pixels, both at the same 3:4 aspect ratio. When a form gives a range instead of one number, the safest choice is usually the top of it. A smaller image inside the accepted range still passes validation, but it’s throwing away resolution the form was willing to accept — and if the photo is ever printed on an admit card or ID document, more source pixels means a sharper result. There’s essentially no downside to submitting 480 × 640 over 240 × 320 as long as the file size still lands in range, so that’s what this page produces by default.
Fitting the 50–200 KB band at a larger pixel size
Because 480 × 640 has four times the pixel area of 240 × 320, it naturally holds more detail per file — which also means it takes a slightly higher JPEG quality setting to look right, and correspondingly more bytes. That works in your favour here: at this pixel size, hitting the 50 KB floor is rarely the problem the way it is for IBPS’s much smaller 200 × 230 photo. The more common adjustment this tool makes at 480 × 640 is trimming quality down to stay under the 200 KB ceiling, especially for photos with a lot of fine detail — patterned clothing, textured backgrounds — that a smaller output size would have simply cropped away.
If your source photo isn’t already in a 3:4 ratio, this tool crops from the centre to reach it, rather than stretching the image out of proportion. A straight-on portrait shot with your face centred in the frame needs the least cropping and gives the most predictable result.