Browser image conversion has two separate requirements: the browser must decode the input and the chosen encoder must create the requested output. Being able to display an AVIF or TIFF does not prove it can export one. Check the actual output type, dimensions and appearance rather than trusting the filename alone.
Start with one supported input
Keep the original and try a representative file before a large batch. JPEG and PNG are useful baseline inputs, but unusual color profiles, large dimensions or damaged files can still cause problems. TIFF decoding is not universal across browsers, and a single thumbnail does not demonstrate support for every TIFF variant.
Understand Canvas fallback behavior
MDN documents that Canvas toBlob exports PNG when the requested type is unsupported. That means a requested filename ending in .avif can still contain PNG data if the tool does not check the result. Changing the extension cannot repair that mismatch. Use an encoder that actually supports the target format or choose a supported output.
Choose which features must survive
JPEG requires a background for transparent pixels. Converting SVG to a raster image fixes its pixel dimensions rather than preserving vector scaling. ZipMyImages handles GIF input as a first-frame still, not an animated export. Keep a dedicated source for animation, multipage or editable work that a still-image pipeline cannot preserve.
Validate a sample before scaling up
Illustrative workflow: convert one transparent logo and one photograph, open both in the destination application, and compare dimensions, edges and actual file type. Check the exported byte size rather than assuming conversion always saves space. If the browser lacks an encoder, use a dedicated converter with the needed capability; repeated retries or lower quality cannot add missing format support.