ProfilePictureChanger.razor

@using Microsoft.AspNetCore.Components.Forms

<AuthorizeView>
    <Authorized>
        <form method="post" enctype="multipart/form-data" action="/user/update-profile-picture">
            @{
                var user = context.User?.Identity?.Name ?? "--noname--";
                var profilePicture = $"/user/{user}.jpg?{Random.Shared.Next()}";
            }
            <label>
                <img src="@(TemporaryPicture ?? profilePicture)" />
                <InputFile name="file" OnChange=ChangeProfilePicture />
                @if (TemporaryPicture == null)
                {
                    <div class="button">change<br>profile picture</div>
                }
            </label>
            <input type="hidden" name="redirectto" value="/">
            @if (TemporaryPicture != null)
            {
                <input type="submit" value="save" />
                <input type="reset" value="cancel" @onclick=CancelChanging />
            }
        </form>
    </Authorized>
</AuthorizeView>

@code {
    string? TemporaryPicture { get; set; }

    async Task ChangeProfilePicture(InputFileChangeEventArgs inputFileChangeEventArgs)
    {
        var image = await inputFileChangeEventArgs.File.RequestImageFileAsync("image/png", 600, 600);
        using Stream imageStream = image.OpenReadStream(1024 * 1024 * 10);
        using MemoryStream ms = new();
        await imageStream.CopyToAsync(ms);
        TemporaryPicture = $"data:image/png;base64,{Convert.ToBase64String(ms.ToArray())}";
    }

    void CancelChanging()
    {
        TemporaryPicture = null;
    }
}

ProfilePictureChanger.razor.css

label {
    display: grid;
    gap: 0;

    margin: 0;
    padding: 0;

    background: #333;
}

.button, input[type=reset] {
    background-color: #222;
    color: #ddd;
    font-size: inherit;
    font-weight: inherit;
    font-family: inherit;
    transition: all .33s linear;
    text-decoration-color: transparent;
    text-align: center;
    cursor: default;
    opacity: initial;
    align-items: center;
    min-height: 2rem;
}

    :is(.button, input[type=reset]):hover {
        border-color: #ddd;
        text-decoration-color: transparent;
        filter: invert();
    }

.button {
    height: 4rem;
    line-height: 1.5rem;
}

label * {
    margin-top: 0 !important;
}

::deep input[type=file] {
    display: none;
}

img {
    place-self: center;
    max-width: 8rem;
    max-height: 8rem;
    object-fit: cover;
}